JPWO2015005420A1 - Piezoelectric sheet, method for producing the sheet, and piezoelectric laminate - Google Patents

Abstract

The present invention relates to a piezoelectric sheet, a method for producing the sheet, and a piezoelectric laminate, wherein the piezoelectric sheet includes a nonwoven fabric or a woven fabric formed using fibers containing an organic polymer, and includes an inorganic filler.

Description

  The present invention relates to a piezoelectric sheet having high piezoelectricity, a method for manufacturing the sheet, and a piezoelectric laminate.

  Conventionally, in order to obtain a polarization structure, a piezoelectric material using a polymer material has been studied to have a porous structure by a method such as foaming or stretching or a crystal structure that is easily polarized. In particular, it is known that when the polymer material has a porous structure, it exhibits high piezoelectric characteristics.

  For example, Patent Document 1 discloses a porous resin sheet for a piezoelectric / pyroelectric element containing ceramic particles having a volume porosity of 20 to 75% and a dielectric constant higher than that of a resin component. Has been. However, since a solvent extraction step is required to remove the phase separation agent used in the production process of the porous resin sheet for piezoelectric / pyroelectric elements, industrial practical application has been difficult.

Patent Document 2 discloses a piezoelectric film that has been subjected to a polarization treatment after forming a rolled film by mixing dielectric fine powder with polytetrafluoroethylene.
Patent Document 3 discloses a piezoelectric element forming sheet material comprising a ceramic component and a thermoplastic resin.
Patent Document 4 discloses an energy conversion film made of a stretched thermoplastic resin film containing an inorganic powder.

JP 2011-216661 JP 61-295678 A JP 2004-339008 A JP 2011-84735 JP

However, the patent document does not describe using a nonwoven fabric or a woven fabric formed using fibers containing an organic polymer as a piezoelectric element.
Under such circumstances, development of a piezoelectric sheet having a higher piezoelectric rate and a piezoelectric laminate using the same is desired.

  An object of the present invention is to provide a piezoelectric sheet having a high piezoelectric rate and a piezoelectric laminate using the sheet.

The present invention relates to the following [1] to [9], for example.
[1] A piezoelectric sheet containing a nonwoven fabric or woven fabric formed using fibers containing an organic polymer and containing an inorganic filler.

[2] The piezoelectric sheet according to [1], wherein the organic polymer is an organic polymer having no dipole due to a molecule and a crystal structure.
[3] The piezoelectric sheet according to [1] or [2], wherein the fiber has an average fiber diameter of 0.05 to 50 μm and a fiber diameter variation coefficient of 0.7 or less.

  [4] The piezoelectric sheet according to any one of [1] to [3], wherein the porosity is 60% or more.

  [5] The piezoelectric sheet according to any one of [1] to [4], wherein the organic polymer is polytetrafluoroethylene.

[6] A method for producing a piezoelectric sheet, comprising a step of producing a fiber by an electrospinning method from a spinning solution containing an organic polymer and an inorganic filler, and forming a nonwoven fabric or a woven fabric from the fiber.
[7] The method for producing a piezoelectric sheet according to [6], wherein the organic polymer is polytetrafluoroethylene.

[8] The piezoelectric sheet according to any one of [1] to [5];
A surface coating layer laminated on at least one of the front and back surfaces of the outer surface of the piezoelectric sheet, and the volume resistivity of the surface coating layer is 1 × 10 ¹³ Ω · cm or more. There is a piezoelectric laminate.
[9] The piezoelectric laminate according to [8], wherein the surface coating layer covers front and back surfaces and end surfaces of the piezoelectric sheet.

  According to the present invention, a piezoelectric sheet and a piezoelectric laminate that have a high porosity, are effective in retaining piezoelectricity, have high flexibility, have a high amount of charge retention in the sheet, and have excellent piezoelectric characteristics. You can get a body.

FIG. 1 is a schematic diagram showing an example of a cross section of the piezoelectric laminate of the present invention. FIG. 2 is a schematic diagram showing an example of a cross section of the piezoelectric laminate of the present invention. FIG. 3 is a schematic diagram showing an example of a cross section of the piezoelectric laminate of the present invention.

  Hereinafter, the piezoelectric sheet, the manufacturing method of the sheet, and the piezoelectric laminate will be described in more detail.

[Piezoelectric sheet]
The piezoelectric sheet of the present invention (hereinafter also referred to as “sheet”) includes a non-woven fabric or a woven fabric formed using fibers containing an organic polymer, and includes an inorganic filler.

<Inorganic filler>
The piezoelectric sheet of the present invention contains an inorganic filler. For this reason, a piezoelectric sheet having a high charge retention amount in the sheet and excellent piezoelectric characteristics can be obtained.
The inorganic filler used in the present invention is preferably a filler having a dielectric constant higher than that of the organic polymer from the viewpoint of obtaining a sheet having a high piezoelectric constant, for example, an inorganic filler having a relative dielectric constant ε of 10 to 10,000. preferable. Specific examples of the inorganic filler include titanium oxide, aluminum oxide, barium titanate, lead zirconate titanate, zirconium oxide, cerium oxide, nickel oxide and tin oxide.

The average particle diameter of the inorganic filler is preferably 1/1000 to 1/2, more preferably 1/100 to 1/10 of the average fiber diameter of the fiber containing the organic polymer. When the average particle diameter of the inorganic filler is within this range, a sheet in which the inorganic filler is uniformly dispersed can be obtained, and the piezoelectric characteristics of the sheet can be improved uniformly.
Here, the average particle diameter can be measured by the following method or an equivalent method.

The average particle diameter of the inorganic filler is obtained by observing with an electron microscope and calculating the average value.
For the average particle size, for example, an SEM (equipment: S-3400N (manufactured by Hitachi High-Technologies Corporation), magnification 10,000 times) observation region is selected at random, and this region is observed by SEM, It can be obtained by randomly selecting 20 inorganic fillers, measuring their particle diameters, and calculating the average.

  The content of the inorganic filler contained in the sheet is preferably 0.1 to 30% by weight, more preferably 0.1 to 15% by weight, and still more preferably 0.1 to 10% by weight with respect to the total amount of the fiber. It is. If the content of the inorganic filler is within the above range, the piezoelectricity of the sheet can be further increased. When the content of the inorganic filler is less than the lower limit value, a sheet having a high piezoelectric rate may not be obtained. When the inorganic filler content is higher than the upper limit value, the initial value of the piezoelectric rate increases, but the charge retention rate May decrease.

<Fiber>
The piezoelectric sheet of the present invention is formed using a fiber containing an organic polymer. For this reason, it is possible to obtain a piezoelectric sheet having a high porosity, effective in retaining piezoelectricity, and having high flexibility.

Examples of the organic polymer constituting the fiber include polymers having a volume resistivity of 1.0 × 10 ¹³ Ω · cm or more. For example, polyamide resins (6-nylon, 6,6-nylon, etc.), aromatic Group polyamide resins (such as aramid), polyolefin resins (such as polyethylene and polypropylene), polyester resins (such as polyethylene terephthalate), polyacrylonitrile, phenolic resins, fluorine resins (such as polytetrafluoroethylene and polyvinylidene fluoride) Imide resin (polyimide, polyamideimide, bismaleimide, etc.). Among them, from the viewpoint of heat resistance and weather resistance, an organic polymer that has a high continuous usable temperature, does not have a dipole due to a molecule and a crystal structure, or does not have a glass transition point in the operating temperature range of the sheet. Preferably there is. The continuously usable temperature can be measured by a continuous use temperature test described in UL746B (UL standard), and is preferably 100 ° C. or higher, and more preferably 200 ° C. or higher. Further, from the viewpoint of moisture resistance, an organic polymer exhibiting water repellency is preferable. As such an organic polymer, polyolefin resin, imide resin, and fluorine resin are preferable, and polytetrafluoroethylene (PTFE) is more preferable.

  The fiber containing the organic polymer preferably has an average fiber diameter of 0.05 to 50 μm, more preferably 0.1 to 20 μm, and still more preferably 0.3 to 5 μm. When the average fiber diameter is within the above range, a non-woven fabric or woven fabric exhibiting high flexibility can be formed, and a sufficient space for holding electric charge can be formed by increasing the fiber surface area. This is preferable in that the distribution uniformity can be increased.

  For example, when the fiber is produced by an electrospinning method, the average fiber diameter is reduced by decreasing the humidity, decreasing the nozzle diameter, increasing the applied voltage, or increasing the voltage density during electrospinning. Tend to be.

  In addition, the average fiber diameter is randomly selected by observing a scanning electron microscope (SEM) region for the fiber (group) to be measured, and observing this region by SEM (magnification: 10,000 times). This is a value calculated based on the measurement results obtained by selecting 20 fibers and measuring the fiber diameter (major axis) of each of these fibers.

The fiber diameter variation coefficient of the fiber is preferably 0.7 or less, more preferably 0.01 to 0.5. When the fiber diameter variation coefficient is within the above range, the fiber diameter of the fiber becomes uniform, and with such a fiber, a sheet having a higher porosity can be obtained, and the charge retention of the obtained sheet can be improved. It is preferable in that it can be increased.
The fiber diameter variation coefficient is calculated from the following equation.
Fiber diameter variation coefficient = standard deviation ÷ average fiber diameter

  The fiber length of the fiber is preferably 0.5 to 100 mm, preferably 1 to 50 mm.

The fiber is produced, for example, by an electrospinning method, a melt spinning method, a melt electrospinning method, a spunbond method (melt blow method), a wet method, or a spunlace method. In particular, the fiber obtained by the electrospinning method has a fiber diameter. Since the nonwoven fabric or woven fabric formed from such fibers has a high porosity and a high specific surface area, a sheet and a piezoelectric laminate having high piezoelectricity can be obtained.
The electrospinning is performed using a spinning solution containing an organic polymer and a solvent, and if necessary, an inorganic filler.

The organic polymer is contained, for example, in an amount of 5 to 100% by weight, preferably 5 to 80% by weight, and more preferably 10 to 70% by weight in the spinning solution, although it depends on the kind of the polymer and the spinning method.
The said organic polymer may be used individually by 1 type, and may use 2 or more types.

When an inorganic filler is blended in the spinning solution, the inorganic filler is included, for example, in an amount of 0.1 to 30% by weight, preferably 1 to 30% by weight in the spinning solution, depending on the type of the inorganic filler. If the content of the inorganic filler is within the above range, the piezoelectricity of the sheet can be further increased. When the content of the inorganic filler is less than the lower limit value, a sheet having a high piezoelectric rate may not be obtained. When the inorganic filler content is higher than the upper limit value, the initial value of the piezoelectric rate increases, but the charge retention rate May decrease.
The said inorganic filler may be used individually by 1 type, and may use 2 or more types.

The solvent is not particularly limited as long as it can dissolve or disperse the organic polymer. For example, water, dimethylacetamide, dimethylformamide, tetrahydrofuran, methylpyrrolidone, xylene, acetone, chloroform, ethylbenzene, cyclohexane, benzene, Examples include sulfolane, methanol, ethanol, phenol, pyridine, propylene carbonate, acetonitrile, trichloroethane, hexafluoroisopropanol, and diethyl ether. These solvents may be used individually by 1 type, and may be used as a mixed solvent which combined 2 or more types.
The solvent is contained in the spinning solution in an amount of, for example, 0 to 90% by weight, preferably 10 to 90% by weight, and more preferably 20 to 80% by weight.

  The spinning solution may further contain additives other than the organic polymer and inorganic filler, such as a surfactant, a dispersant, a charge adjusting agent, a functional particle, an adhesive, a viscosity adjusting agent, and a fiber forming agent. Good. In the spinning solution, when the solubility of the organic polymer in the solvent is low (for example, when the organic polymer is PTFE and the solvent is water), fiber formation is performed from the viewpoint of maintaining the organic polymer in a fiber shape during spinning. It is preferable that an agent is included.

  Examples of the surfactant include a fluorine-based surfactant (that is, a surfactant having a fluorine atom. For example, an ammonium salt of an acid having a perfluoroalkyl group), a hydrocarbon-based surfactant (the main chain is an alkyl group). And a surfactant based on silicon (a surfactant having a silicon atom).

If it is a commercial item as said fluorosurfactant, it is a footgent (registered trademark) 100 (anionic fluorosurfactant), a footgent (registered trademark) 310 (cationic fluorosurfactant). (Above, manufactured by Neos Co., Ltd.), Megafac F114 (anionic fluorine surfactant, manufactured by DIC Corporation), Surflon S-231 (amphoteric fluorine surfactant, manufactured by Asahi Glass Co., Ltd.), etc. Is mentioned.
When the surfactant is blended, the amount used is, for example, 0.01 to 5% by weight, preferably 0.1 to 3% by weight in the spinning solution.

The fiber forming agent is preferably a polymer having high solubility in a solvent, such as polyethylene oxide, polyethylene glycol, dextran, alginic acid, chitosan, starch, polyvinylpyrrolidone, polyacrylic acid, polymethacrylic acid, polyacrylamide. , Cellulose, and polyvinyl alcohol.
The amount of the fiber-forming agent used is, for example, 0.1 to 15% by weight, preferably 1 to 10% by weight in the spinning solution, although it depends on the viscosity of the solvent and the solubility in the solvent.

  The spinning solution can be produced by mixing the above-described organic polymer, solvent and, if necessary, additives by a conventionally known method.

When the organic polymer is PTFE, the spinning solution preferably contains PTFE, a fiber forming agent, and a solvent.
Preferable examples of such spinning liquid include the following spinning liquid (1) (when no inorganic filler is included) and spinning liquid (2) (when an inorganic filler is included).
Spinning liquid (1): Spinning liquid containing 30 to 70% by weight, preferably 35 to 60% by weight of PTFE, and 0.1 to 10% by weight, preferably 1 to 7% by weight of a fiber forming agent. Spinning liquid (2) : 1-30 wt%, preferably 1-20 wt% of inorganic filler, 30-60 wt%, preferably 35-55 wt% of PTFE, 0.1-10 wt% of fiber former, preferably Spinning solution containing 1-7% by weight

The applied voltage when performing this electrospinning is preferably 5 to 50 kV, more preferably 10 to 40 kV.
The tip diameter (outer diameter) of the spinning nozzle is preferably 0.1 to 2.0 mm, more preferably 0.2 to 1.6 mm, and still more preferably 0.3 to 1.6 mm.
More specifically, for example, when the spinning solution (1) is used, the applied voltage is preferably 10 to 50 kV, more preferably 10 to 40 kV, and the tip diameter (outer diameter) of the spinning nozzle is used. ) Is preferably 0.2 to 1.6 mm.
Moreover, the distance between electrodes is 50-800 mm normally, Preferably, it is about 100-350 mm.

As a method for producing the fiber, a method for producing a fiber made of PTFE by an electrospinning method will be specifically described. As a method for producing the PTFE fiber, a conventionally known production method can be employed, and examples thereof include the following methods described in JP-T-2012-515850.
Providing a spinning solution comprising PTFE, a fiber forming agent and a solvent and having a viscosity of at least 50,000 cP;
Spinning the spinning solution from a nozzle and forming a fiber by electrostatic traction;
Collecting the fibers on a collector (eg, a take-up spool) to form a precursor;
The method comprising calcining the precursor to form PTFE fibers by removing the solvent and the fiber-forming agent. In this method, an inorganic filler is added to the spinning solution to thereby add PTFE containing the inorganic filler. Fiber can be obtained.

<Method for manufacturing piezoelectric sheet>
The method for producing the sheet of the present invention is not particularly limited as long as a piezoelectric sheet containing a nonwoven fabric or woven fabric formed using a fiber containing an organic polymer and containing an inorganic filler is obtained. In addition to the method of supporting an inorganic filler on the formed nonwoven fabric or woven fabric, for example, an inorganic filler is blended in the spinning solution, and a fiber containing the inorganic filler is produced by an electrospinning method, and then the inorganic filler is produced. Examples thereof include a method of forming a nonwoven fabric or a woven fabric from a fiber containing a filler. That is, the aspect of the sheet of the present invention includes an aspect in which an inorganic filler is dispersed in a fiber and an aspect in which an inorganic filler is supported (attached or bonded) on the fiber surface. From the viewpoint of long-term practicality, the sheet of the present invention is a non-woven fabric or woven fabric composed of fibers containing an inorganic filler to prevent the inorganic filler from falling off during storage and use (under stress). This is preferable.

  In order to form the non-woven fabric, the step of producing the fiber, and the step of collecting the fiber (in the presence of an inorganic filler if necessary) and forming the non-woven fabric may be performed separately, They may be performed simultaneously (that is, the fibers may be accumulated in a sheet form while being produced to form a nonwoven fabric). Specifically, for example, using the electrospinning method, the step of producing the fiber, and the step of collecting the fiber (in the presence of an inorganic filler if necessary) to form a nonwoven fabric are simultaneously performed. Alternatively, for example, after performing the step of manufacturing the fiber, a step of accumulating the fiber in a sheet form (in the presence of an inorganic filler if necessary) by a wet method to form a nonwoven fabric may be performed.

In order to form the woven fabric, it can be produced by a method including a step of producing the fiber, and a step of weaving the obtained fiber into a sheet (in the presence of an inorganic filler if necessary) to form a woven fabric. .
As a method for weaving the fiber into a sheet (if necessary, in the presence of an inorganic filler), a conventionally known weaving method can be used, and methods such as a water jet loom, an air jet loom, and a rapier room can be used.

  When the inorganic filler is used in the nonwoven fabric or woven fabric forming step, the content of the inorganic filler is 0.1 to 30% by weight, preferably 1 to 30% by weight, based on the total amount of the fiber. If it is in the said range, the piezoelectric rate of a piezoelectric sheet can be raised more.

  After forming the nonwoven fabric or woven fabric, it is preferable to perform a heat treatment. In particular, when the organic polymer is PTFE, it is preferable to perform this heat treatment. The said heat processing is performed by heat-processing the nonwoven fabric or woven fabric formed from the fiber obtained with the spinning solution containing a fiber forming agent and a solvent normally on 200-390 degreeC and the conditions for 30 to 300 minutes, for example. Can do. By this heat treatment, the solvent and the fiber-forming agent remaining on the nonwoven fabric or woven fabric are removed, and the nonwoven fabric or woven fabric made of only PTFE (when the spinning solution contains an inorganic filler, the inorganic filler is also included). Can be manufactured.

Below, the process of accumulating the said fiber in a sheet form with a wet method and forming a nonwoven fabric is demonstrated.
As a method for forming a nonwoven fabric by a wet method, for example, an aqueous dispersion containing the fiber may be deposited on a mesh, for example, and formed into a sheet shape.

  The amount of the fiber used is preferably 0.1 to 10% by weight, more preferably 0.1 to 5% by weight, based on the total amount of the dispersion. If the fiber is used within this range, water can be efficiently utilized in the accumulation (papermaking) process, and the dispersion state of the fiber is improved, so that a uniform wet nonwoven fabric can be obtained.

An inorganic filler may be blended in the aqueous dispersion.
When the inorganic filler is blended in the aqueous dispersion, the amount of the inorganic filler used is preferably 0.01 to 10% by weight, more preferably 0.01 to 1.5% by weight, based on the total amount of the aqueous dispersion. It is. When the inorganic filler is used in an amount within this range, a uniform and large amount of inorganic filler can be supported in the obtained wet nonwoven fabric.

  In order to improve the dispersion state, the aqueous dispersion is added with a dispersing agent such as a cationic, anionic, or nonionic surfactant, an oil agent, or an antifoaming agent that suppresses the generation of bubbles. Also good.

  Specifically, the sheet manufacturing method of the present invention includes (1) a method of supporting an inorganic filler on a nonwoven fabric or a woven fabric obtained by forming the fiber into a sheet, and (2) an inorganic filler using an electrospinning method. A method of producing a fiber containing an inorganic filler from a spinning solution containing a non-woven fabric or a woven fabric, and (3) a method of forming a non-woven fabric from an aqueous dispersion containing an inorganic filler using a wet method. Can be mentioned. Among these, from the point that a large amount of inorganic filler can be contained in the nonwoven fabric, (2) a method of producing a nonwoven fabric by producing an inorganic filler-containing fiber from a spinning solution containing an inorganic filler using an electrospinning method Is preferred.

Below, after forming a nonwoven fabric or a woven fabric, the process of carrying | supporting an inorganic filler is demonstrated.
The method of supporting the inorganic filler after forming the nonwoven fabric or woven fabric from the fibers is not particularly limited, and may be performed by a conventionally known method. For example, the nonwoven fabric or woven fabric is dispersed in a dispersion in which the inorganic filler is dispersed. The method of immersing is mentioned. At this time, the surface of the nonwoven fabric or woven fabric or the inorganic filler may be treated in advance with a hydrophilizing agent or a coupling agent. In addition, when immersing the nonwoven fabric or woven fabric in the dispersion and when drying the dispersion adhered to the nonwoven fabric or woven fabric after the immersion, temperature or pressure may be applied. It can be adjusted appropriately.
In this case, the supported amount of the inorganic filler is preferably 0.1 to 30% by weight, more preferably 1 to 20% by weight, based on the total weight of the nonwoven fabric or woven fabric.

  In the manufacturing process of the piezoelectric sheet, when an inorganic filler is used in a plurality of steps, the amount of the inorganic filler is preferably 0.1 to 30% by weight based on the total amount of the fiber, the total amount of the inorganic filler, The amount is more preferably 0.1 to 15% by weight, and still more preferably 0.1 to 10% by weight. If the inorganic filler is within the above range, the piezoelectricity can be further increased while maintaining the flexibility of the piezoelectric sheet.

(Piezoelectric sheet)
Basis weight of the sheet of the present invention is preferably 500 g / m ² or less, more preferably 300 g / m ² or less, more preferably 100 g / m ² or less, particularly preferably 0.1 to 20 g / m ^2.
The thickness of the sheet | seat of this invention is 10 micrometers-1 mm normally, Preferably it is 50 micrometers-500 micrometers.
The fabric weight and thickness tend to increase when the fiber is produced by, for example, electrospinning, for example, by increasing the spinning time or increasing the number of spinning nozzles. Tends to increase by increasing the number of depositions, increasing the fiber concentration in the aqueous dispersion.

The porosity of the non-woven fabric or woven fabric obtained by the method (1) before supporting the inorganic filler is preferably 62% or more, more preferably 77% or more, and further preferably 80 to 99%. The porosity of the sheet of the present invention is preferably 60% or more, more preferably 75% or more, and further preferably 80 to 98%. When the porosity is within the above range, it is preferable in that the charge retention rate is increased.
The porosity of the nonwoven fabric or woven fabric made of PTFE when the organic polymer is PTFE is calculated by the following method.
(True density of PTFE−apparent density) × 100 / true density of PTFE

  The sheet of the present invention may be either a single layer or a sheet composed of two or more layers having different materials and fiber diameters.

(Polarization treatment)
The sheet obtained as described above can be subjected to polarization treatment to inject charges into the sheet. As the method for the polarization treatment, a conventionally known method can be used, and is not particularly limited, and examples thereof include voltage application processing such as DC voltage application processing and AC voltage application processing, and corona discharge processing.
The injected charge is concentrated in the pores existing in the nonwoven fabric or woven fabric to induce polarization.
The internally polarized sheet can take out electric charges through the front and back surfaces of the sheet by applying a compressive load in the sheet thickness direction. That is, charge transfer occurs with respect to the external load (electric circuit), and an electromotive force is obtained.

[Piezoelectric laminate]
The piezoelectric laminate according to the present invention includes the piezoelectric sheet, and a surface coating layer laminated on at least one of the front and back surfaces of the outer surface of the piezoelectric sheet, and the surface coating layer The volume resistivity is 1 × 10 ¹³ Ω · cm or more.
Since the surface covering layer works to prevent the electric charge held in the piezoelectric sheet from being attenuated by being electrically connected to the external environment, it is effective for holding the piezoelectric rate of the piezoelectric laminate of the present invention. Function.

<Surface coating layer>
(Volume resistivity)
The volume resistivity of the surface coating layer is usually 1 × 10 ¹³ Ω · cm or more, preferably 1 × 10 ¹⁴ Ω · cm or more. If it exists in this range, it is preferable at the point of the improvement of the long-term charge retention in a piezoelectric sheet.
The volume resistivity can be measured based on the double ring electrode method using a single surface coating layer (film).

(Elastic modulus)
The elastic modulus of the surface coating layer is preferably different from that of the piezoelectric sheet, and may be higher or lower than that of the piezoelectric sheet. In this case, the difference in elastic modulus between the surface coating layer and the piezoelectric sheet is usually 10 MPa or more, preferably 50 MPa or more. If it exists in this range, it is preferable at the point which can induce a nonlinear deformation at the time of sheet compression.

(Relative permittivity)
The surface coating layer preferably has a relative dielectric constant of usually 2 to 100.
If the relative dielectric constant is within this range, when the electric charge is applied by the polarization treatment, specifically, corona discharge, the electric charge is concentrated inside the surface coating layer having a high dielectric constant, and the surface coating layer and the piezoelectric layer are piezoelectric. Charge is also retained at the interface of the conductive sheet.

(thickness)
The thickness of the surface coating layer is usually 1 μm or more, and preferably 30% or less of the thickness of the piezoelectric sheet. When the thickness is 1 μm or less, the handleability of the film for the surface coating layer is poor, and problems such as a decrease in insulation due to film defects (pinholes) may occur. In addition, when the thickness is 30% or more of the thickness of the piezoelectric sheet, the cost for injecting charges into the piezoelectric sheet is increased, and specifically, the corona discharge voltage is set high. Therefore, the industrial application tends to be difficult.

  When the surface coating layer is formed on both surfaces of the piezoelectric sheet, if the thickness of each surface coating layer is made different from each other, nonlinear deformation is induced with respect to compressive strain, and high piezoelectricity is exhibited. This is preferable because it is possible.

(material)
The material of the surface coating layer is not particularly limited as long as it has the above physical properties, and examples thereof include a thermosetting resin and a thermoplastic resin. Examples of thermosetting resins include polyimide, epoxy resin, thermosetting rubber (eg, vinylidene fluoride rubber, silicone rubber), polyurethane, phenol resin, imide resin (eg, polyimide, polyamideimide, bismaleimide), silicone resin. Is mentioned. Examples of the thermoplastic resin include acrylic resin, methacrylic resin, polypropylene, polyamide, vinyl chloride resin, silicone resin, fluorine resin (for example, polychlorotrifluoroethylene (PCTFE), ethylene-tetrafluoroethylene copolymer (ETFE), Polyvinylidene fluoride (PVDF), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP)), nylon, polystyrene, high density polyethylene, low density polyethylene, polyphenylene Examples thereof include sulfide, polyethylene oxide, polysulfone, and polyvinylidene chloride.

(Method for forming surface coating layer)
The surface coating layer can be formed by a conventionally known method. For example, when a thermosetting resin is used, at least one side of the front and back surfaces of the piezoelectric sheet, that is, one side or both sides, is cured with the thermosetting resin. It can be formed by applying and drying a solution obtained by dissolving an agent in a solvent. Moreover, it can also form by apply | coating a photocurable resin and making it harden | cure.
The surface coating layer preferably covers the front and back surfaces of the piezoelectric sheet from the viewpoint of obtaining a piezoelectric laminate that retains electric charge for a long time and retains a high piezoelectric rate. The back surface and the end surface are preferably covered.
In the present invention, the “front and back surfaces of the piezoelectric sheet” means two surfaces having the largest area among the outer surfaces (six surfaces) of the sheet, and the “end surface of the piezoelectric sheet” Of the outer surfaces (six surfaces) of the sheet, the four surfaces excluding the front and back surfaces.

As the curing agent (crosslinking agent), a conventionally known curing agent can be used. For example, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane (trade name: Perhexa 25B (NOF) Product)), triallyl isocyanurate (trade name: TAIC (manufactured by NOF Corporation)).
The usage-amount of a hardening | curing agent is 1 to 20 weight% normally with respect to 100 weight part of said resin, Preferably it is 1 to 10 weight%.

Examples of the solvent used here include tetrahydrofuran (THF), toluene, benzene, acetone, and ethylbenzene.
The usage-amount of a solvent is 100-5000 weight part normally with respect to 100 weight part of said resin, Preferably it is 200-3000 weight part.

  As described above, the surface coating layer may be formed (laminated) by directly applying a liquid containing a thermosetting resin and a curing agent to the surface of the piezoelectric sheet and drying it. A method of forming a surface coating layer (film for) and laminating it by thermocompression bonding with the piezoelectric sheet may be used.

  When the surface coating layer (film for) is formed in advance, a thermoplastic resin, a thermosetting resin or a photocurable resin is formed by a conventionally known molding method, for example, a molding machine such as a single-screw or twin-screw extruder. And after mixing a hardening | curing agent and a solvent as needed, the method of shape | molding in a film form etc. with a pressure molding machine, T-die, etc. is mentioned, for example. In the case of a thermoplastic resin, the molding temperature is usually about the same as the melting temperature of the resin, and in the case of a thermosetting resin, it is usually about the same as the curing temperature of the resin.

As the piezoelectric laminate of the present invention, a surface coating layer is laminated on one side of a piezoelectric sheet (FIG. 1), a surface coating layer is laminated on the front and back surfaces of a piezoelectric sheet (FIG. 2), piezoelectricity Examples include those in which a surface coating layer is formed on the front and back surfaces and end surfaces of the sheet (FIG. 3).
The piezoelectric laminate according to the present invention can form a new interface capable of holding electric charges between the piezoelectric sheet and the surface coating layer, and thus is effective in improving the piezoelectric rate and is held at such an interface. The amount of charges that can be held synergistically by moving the charges to the hollow structure of the piezoelectric sheet is increased, which contributes to an improvement in piezoelectricity.

  The piezoelectric laminate of the present invention includes a non-woven fabric or a woven fabric formed using a fiber containing an organic polymer, and contains a piezoelectric sheet containing an inorganic filler, so that it has high flexibility and charge response even at a minute stress. Produce. For this reason, the piezoelectric laminated body of the present invention has an electromotive force generated by pressure, vibration, sensing materials such as actuators, vibration bodies, pressure sensors, vibration force sensors, and pressure sensors that can be used in automobiles, outdoors, and factories. It can be used as a power generation material used as a power source. Furthermore, a method of storing the electromotive force in a power storage mechanism and using it is also included.

The piezoelectric laminate of the present invention can induce a non-linear deformation with respect to the compressive strain at the time of charge extraction by providing a difference in elastic modulus between the piezoelectric sheet and the surface coating layer. About 100 to 400 (unit: d ₃₃ (pC / N)) can be indicated.

  In the piezoelectric laminate of the present invention, a conventionally known layer or the like other than the piezoelectric sheet and the surface coating layer may exist.

  Next, although an Example is shown and this invention is demonstrated further in detail, this invention is not limited by these.

[Example 1] Production of piezoelectric sheet and piezoelectric laminate comprising titanium oxide-containing PTFE fiber obtained by electrospinning (titanium oxide content: 20 wt%)
A piezoelectric sheet which is a nonwoven fabric sheet is obtained by accumulating PTFE fibers containing titanium oxide in a sheet shape by the electrospinning method described in JP-T-2012-515850 using the following spinning solution and then heat-treating the sheet. (Piezoelectric layer) was manufactured.

(Spinning liquid)
PTFE aqueous dispersion (concentration: 60% by weight) 100 parts by weight Polyethylene oxide (molecular weight 300,000) 8 parts by weight Titanium oxide aqueous dispersion (concentration: 40% by weight) 38 parts by weight

<Measurement of average fiber diameter and fiber diameter standard deviation>
For the piezoelectric sheet, a region for SEM observation was randomly selected, and this region was subjected to SEM observation (apparatus: S-3400 (manufactured by Hitachi High-Technologies Corporation), magnification 10,000 times) to randomly select 20 fibers. The average fiber diameter (arithmetic) and fiber diameter standard deviation were calculated based on the measurement results of these fibers.
The fiber diameter variation coefficient was calculated from the following formula.
Fiber diameter variation coefficient = standard deviation ÷ average fiber diameter

<Measurement of porosity>
The porosity was measured based on the following method.
Apparent appearance calculated using the weight of a test piece cut out of a 4 cm square (4 cm length, 4 cm width) of a piezoelectric sheet and the thickness measured by a micrometer (LITEMATEC VL-50, manufactured by Mitutoyo Corporation) It calculated by the following formula using the density.
{(True density of PTFE × PTFE content ratio + true density of inorganic filler × inorganic filler content ratio) −apparent density} × 100 / (true density of PTFE × PTFE content ratio + true density of inorganic filler × inorganic filler content ratio) )
At this time, PTFE content ratio + inorganic filler content ratio = 100%.

(Formation of surface coating layer)
Thermosetting resin (fluorine rubber G912 manufactured by Daikin Industries, Ltd.) (fluorine concentration: 70.5% by weight, specific gravity (23 ° C): 1.91 (JISK6268), Mooney viscosity (on the front and back surfaces and end surfaces of the obtained piezoelectric sheet) ML1 + 10 · 100 ° C): about 77 (JISK6300-1)) 10g, triallyl isocyanurate (trade name: TAIC, NOF Corporation) 0.5g, 2,5-dimethyl-2 as a curing agent , 5-di (t-butylperoxy) hexane (trade name: Perhexa 25B, manufactured by NOF Corporation) and 0.1 g of a solvent (THF) manufactured by Wako Pure Chemical Industries, Ltd. Apply and dry using an applicator, and vulcanize by heating at 160 ° C. for 15 minutes to form a surface coating layer having a low elastic modulus on both the front and back surfaces and the end surface of the piezoelectric sheet, thereby obtaining a piezoelectric laminate. It was.

The volume resistivity of this surface coating layer was 1.0 × 10 ¹³ Ω · cm. Hereinafter, the volume resistivity of the surface coating layer used in the examples is also the same value.
The volume resistivity of the surface coating layer was measured based on the double ring electrode method using the surface coating layer alone.

<Preparation of sample for evaluation>
The piezoelectric laminate was subjected to polarization treatment by corona discharge for 3 minutes at room temperature with a distance of 12.5 mm between electrodes and a voltage between electrodes of 3 kV using a corona discharge device manufactured by Kasuga Electric Co., and then both sides of the laminate. A rectangular electrode made of aluminum foil (manufactured by Mitsubishi Aluminum Co., Ltd., FOIL, 11 μm) was provided to prepare a sample for evaluation.

<Measurement of piezoelectricity>
A constant AC acceleration α (frequency: 90 to 300 Hz, size: 2 to 10 m / s ² ) was applied in the thickness direction of the sample for evaluation under conditions of room temperature and 20% humidity. Was measured, and the initial piezoelectric constant d ₃₃ (pC / N) was measured (this time is defined as day 0). After measuring the initial piezoelectric constant, leave the charged sample for evaluation in an atmosphere of room temperature (20 ° C.) and humidity 20%, and measure the piezoelectric constant in the same way after 1 day, 5 days, or 6 days. did. These results are shown in Table 1 or Table 2.

[Example 2] Production of piezoelectric sheet and piezoelectric laminate comprising titanium oxide-containing PTFE fibers obtained by electrospinning (titanium oxide content: 10 wt%)
A piezoelectric sheet and a piezoelectric laminate were produced by performing the same operations as in Example 1 except that the following spinning solution was used, and the same physical properties as in Example 1 were measured using these. The results are also shown in Table 1.

(Spinning liquid)
PTFE aqueous dispersion (concentration: 60% by weight) 100 parts by weight Polyethylene oxide (molecular weight 300,000) 7 parts by weight Titanium oxide aqueous dispersion (concentration: 40% by weight) 17 parts by weight

[Reference Example 1] Production of piezoelectric sheet and piezoelectric laminate comprising PTFE fiber obtained by electrospinning method (containing no inorganic filler)
A piezoelectric sheet and a piezoelectric laminate were produced by performing the same operations as in Example 1 except that the following spinning solution was used, and the same physical properties as in Example 1 were measured using these. The results are also shown in Table 1.

(Spinning liquid)
PTFE aqueous dispersion (concentration: 60% by weight) 100 parts by weight Polyethylene oxide (molecular weight 300,000) 5 parts by weight

Reference Example 2 Production of Piezoelectric Laminate Using Expanded PTFE Film Instead of a piezoelectric sheet, an expanded PTFE film (manufactured by Nippon Valqua Industries, Ltd., porosity 78%, average pore diameter 0.30 μm, thickness A piezoelectric laminate was manufactured by performing the same operation as in Example 1 except that 50 μm) was used, and the same physical properties as in Example 1 were measured using the expanded PTFE film and the obtained piezoelectric laminate. The results are also shown in Table 1.

[Example 3] Production of piezoelectric sheet and piezoelectric laminate comprising titanium oxide-containing PTFE fibers obtained by electrospinning (titanium oxide content: 5 wt%)
A piezoelectric sheet and a piezoelectric laminate were produced by performing the same operations as in Example 1 except that the following spinning solution was used, and the same physical properties as in Example 1 were measured using these. The results are also shown in Table 2.

(Spinning solution)
PTFE aqueous dispersion (concentration: 60% by weight) 100 parts by weight Polyethylene oxide (molecular weight 300,000) 6 parts by weight Titanium oxide aqueous dispersion (concentration: 40% by weight) 8 parts by weight

[Example 4] Production of piezoelectric sheet and piezoelectric laminate comprising titanium oxide-containing PTFE fiber obtained by electrospinning (titanium oxide content: 1 wt%)
A piezoelectric sheet and a piezoelectric laminate were produced by performing the same operations as in Example 1 except that the following spinning solution was used, and the same physical properties as in Example 1 were measured using these. The results are also shown in Table 2.

(Spinning liquid)
PTFE aqueous dispersion (concentration: 60% by weight) 100 parts by weight Polyethylene oxide (molecular weight 300,000) 5 parts by weight Titanium oxide aqueous dispersion (concentration: 40% by weight) 1.5 parts by weight

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric laminated body 2 ... Piezoelectric sheet 3 ... Surface coating layer

Claims (9)

  A piezoelectric sheet comprising a nonwoven fabric or a woven fabric formed using a fiber containing an organic polymer, and an inorganic filler.   The piezoelectric sheet according to claim 1, wherein the organic polymer is an organic polymer having no dipole due to a molecular structure and a crystal structure.   The piezoelectric sheet according to claim 1 or 2, wherein an average fiber diameter of the fibers is 0.05 to 50 µm, and a fiber diameter variation coefficient is 0.7 or less.   The piezoelectric sheet according to any one of claims 1 to 3, wherein the porosity is 60% or more.   The piezoelectric sheet according to claim 1, wherein the organic polymer is polytetrafluoroethylene.   A method for producing a piezoelectric sheet, comprising a step of producing a fiber by an electrospinning method from a spinning solution containing an organic polymer and an inorganic filler, and forming a nonwoven fabric or a woven fabric from the fiber.   The method for producing a piezoelectric sheet according to claim 6, wherein the organic polymer is polytetrafluoroethylene. The piezoelectric sheet according to any one of claims 1 to 5,
A surface coating layer laminated on at least one of the front and back surfaces of the outer surface of the piezoelectric sheet, and the volume resistivity of the surface coating layer is 1 × 10 ¹³ Ω · cm or more. There is a piezoelectric laminate.   The piezoelectric laminate according to claim 8, wherein the surface coating layer covers front and back surfaces and end surfaces of the piezoelectric sheet.

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