TW202103344A - Piezoelectric sensor and method of manufacturing piezoelectric sensor - Google Patents

Abstract

An objective of the present invention is to provide a piezoelectric sensor that exhibits a high output voltage even during long-term use.

One embodiment of the present invention relates to a piezoelectric sensor and a method of manufacturing the piezoelectric sensor, the piezoelectric sensor including a metal layer, a piezoelectric layer, and a conductive coating layer in this order, wherein the ratio of the bending rigidity of the metal layer to the bending rigidity of the conductive coating layer is 10 to 100.

Description

Piezoelectric sensor and manufacturing method of piezoelectric sensor

An embodiment of the present invention relates to a piezoelectric sensor and a manufacturing method of the piezoelectric sensor.

Piezoelectric sensors (mat sensors) are often used to detect the entry and exit of people or objects.

Such a piezoelectric sensor is disclosed in Patent Document 1. A piezoelectric sensor is laminated with a signal electrode made of aluminum foil on one side of a piezoelectric sheet, and a signal electrode made of aluminum foil is laminated on the other side. It is made of grounding electrode.

Patent Document 2 also discloses a piezoelectric sensor in which electrode layers including an elastomer and a conductive material are provided on both sides of a piezoelectric layer.

[Prior Technical Literature]

〔Patent Literature〕

[Patent Document 1] JP 2017-179126 A

[Patent Document 2] WO 2017/010135

After verification, the inventor found that the conventional piezo-inductance sensor disclosed in the aforementioned patent document will have a reduced output voltage if it is used for a long period of time, and depending on the circumstances, the output voltage may be so low that it can no longer be used as a piezo-inductor. The extent to which the measuring device is used.

As mentioned above, if the output voltage is reduced, it cannot be distinguished from noise, and false detection is prone to occur, and the piezoelectric sensor must be replaced frequently.

An embodiment of the present invention provides a piezo-inductance sensor that exhibits a high output voltage even in long-term use.

Under such circumstances, the inventors of the present invention have devoted themselves to the research in order to solve the aforementioned problems. As a result, they have found that the aforementioned problems can be solved according to the following configuration examples.

The configuration example of the present invention is as follows:

[1] Piezoelectric sensor includes a metal layer, a piezoelectric layer and a conductive coating layer in sequence, among which,

The ratio of the bending rigidity of the aforementioned metal layer to the bending rigidity of the aforementioned conductive coating film layer is 10-100.

[2] The piezoelectric sensor according to [1] above, wherein the conductive coating layer is a layer containing a conductive filler and a binder.

[3] The piezoelectric sensor according to [1] or [2] above, wherein the piezoelectric layer is a non-woven fabric or woven fabric containing an organic polymer, and the organic polymer does not have a molecular or crystalline structure. The dipole.

[4] The piezoelectric sensor according to [3] above, wherein the organic polymer is polytetrafluoroethylene.

[5] The piezoelectric sensor according to [3] or [4] above, wherein the average fiber diameter of the fibers constituting the non-woven fabric or woven fabric is 0.05 to 50 μm.

[6] The piezoelectric sensor according to any one of [3] to [5] above, wherein the fiber diameter variation coefficient of the fibers constituting the non-woven fabric or woven fabric is 0.7 or less.

[7] The piezoelectric sensor according to any one of [1] to [6] above, wherein the piezoelectric layer has a porosity of 0.1 to 70% by volume.

[8] A method for manufacturing a piezoelectric sensor comprising a metal layer, a piezoelectric layer, and a conductive coating layer in sequence, which includes: coating a composition containing conductive fillers and a bonding agent on the piezoelectric layer, and then The step of drying or hardening the coated composition.

According to an embodiment of the present invention, even in the initial and long-term use, a piezoelectric sensor showing high output voltage can be obtained, and long-term reliability can be obtained. Specifically, even in long-term use, it can be easily discriminated and detected. The pressure and noise of the subject are rarely detected by piezoelectric sensors.

"Piezoelectric Sensor"

The piezoelectric sensor of an embodiment of the present invention (hereinafter referred to as "the sensor") includes a metal layer, a piezoelectric layer, and a conductive coating layer in this order, wherein the bending rigidity of the metal layer is The ratio of the flexural rigidity of the aforementioned conductive coating film layer (flexural rigidity of the metal layer/flexural rigidity of the conductive coating film layer) is 10 to 100.

Because this sensor uses a metal layer and a conductive coating layer, it has the aforementioned bending stiffness ratio. Since the layer sandwiching the piezoelectric layer has such a bending stiffness ratio, even if it is used in the initial and long-term Piezoelectric sensors that display high output voltages can be obtained, and long-term reliability can be obtained. Specifically, even long-term use, the pressure and noise of the detection object can be easily distinguished, and the piezoelectricity of the detection object is rarely detected incorrectly. Detector.

In the present invention, the so-called "long-term use" refers to, for example, a situation where the sensor is pressed more than 1000 times as in the following embodiment.

Although the reason why this sensor produces such an effect is not clear, it can be assumed that the deformation of the upper surface side and the lower surface side of the piezoelectric layer is different when the sensor is pressed. The sensor will display a high output voltage, and it can be assumed that the plastic deformation of the piezoelectric layer can be suppressed, so the sensor will display a high output voltage for a long time.

From the point of view of a sensor that displays a higher output voltage even in the initial and long-term use, the aforementioned bending stiffness ratio is 10 or more and 100 or less, preferably 20 or more, and more preferably 30 or more. Preferably, it is 70 or less, more preferably 60 or less, and particularly preferably 50 or less.

The ratio of bending rigidity can be specifically measured by the method disclosed in the following examples.

The sensor is configured such that the pressure is applied to the side of the metal layer and the user is better. In this way, the sensor can further suppress the plastic deformation of the piezoelectric layer, and therefore, a sensor displaying a high output voltage can be easily obtained even after a longer period of time.

The sensor is not particularly limited to include a metal layer, a piezoelectric layer, and a conductive coating layer. It may also contain conventional layers such as an adhesive layer between these layers as needed, but it is preferably There is a metal layer on one side of the largest surface of the electrical layer, and a conductive coating layer on the other side of the largest surface of the piezoelectric layer. More preferably, the metal layer is directly connected to the side of the largest surface of the piezoelectric layer. The sexual coating layer is directly connected to the other side of the largest surface of the piezoelectric layer. In other words, the ratio of the bending rigidity of the two layers adjacent to the largest surface of the piezoelectric layer is preferably within the aforementioned range.

In addition, the sensor may have conventional layers of conventional piezoelectric sensors, such as an insulating layer, an electrode layer other than the aforementioned metal layer and conductive coating layer, etc. Components for taking electricity, etc.

The method of manufacturing this sensor is not particularly limited as long as a laminate including a metal layer, a piezoelectric layer, and a conductive coating layer can be obtained in this order. For example, the following conductive paints can be coated on An insulator such as an insulating layer, and then the resulting insulator with a conductive coating layer is laminated so that the conductive coating layer becomes the piezoelectric layer side, or the following conductive paint, etc. is coated on the support Then, the conductive coating film layer peeled from the obtained support with the conductive coating film layer is laminated with the piezoelectric, but it can be obtained with good manufacturing ease, and both in the initial and long-term use From the point of view that a sensor with a high output voltage can be easily obtained with a sensor with good long-term reliability, the following manufacturing method is preferred.

In the case of using an insulator with a conductive coating layer as described above, the insulator is not considered in the calculation of the ratio of bending stiffness.

This sensor is a sensor for detecting pressure, suitable for pedal sensors, impact sensors, pulse wave and other biological sensors, seat sensors, etc.

<Metal layer>

The aforementioned metal layer is not particularly limited, and electrodes used in conventional piezoelectric sensors can be used.

The shape, size, etc. of the aforementioned metal layer may be appropriately selected depending on the intended use, and there is no particular limitation.

The metal constituting the aforementioned metal layer is not particularly limited, and can be, for example, lithium, beryllium, magnesium, calcium, strontium, barium, boron, aluminum, gallium, indium, antimony, tin, silver, gold, copper, nickel, palladium, platinum , Chromium, molybdenum, tungsten, manganese, cobalt, alloys of the metals listed above. Among them, particularly suitable ones are aluminum, copper, silver, and nickel.

The aforementioned metal layer is preferably a commercially available metal plate (foil) from the viewpoints of the ease of manufacture of the sensor and the possibility of easily obtaining a sensor having a bending rigidity ratio within the aforementioned range.

From the point of view that a sensor that displays high output voltage can be obtained even during initial and long-term use, the value of the bending rigidity of the aforementioned metal layer is preferably 10 GPa or more, more preferably 40 GPa or more, and even better It is 50 GPa or more, preferably 300 GPa or less, and more preferably 200 GPa or less.

The thickness of the aforementioned metal layer is not particularly limited. It can be the same thickness as the conventional electrode, but it is preferably a thickness capable of keeping the bending rigidity in the aforementioned range, since it can be easily manufactured. From the viewpoint of a desired sensor, etc., it is preferably 0.001 mm or more, more preferably 0.01 mm or more, more preferably 1 mm or less, and more preferably 0.1 mm or less.

<Conductive coating layer>

The aforementioned conductive coating film layer is not particularly limited as long as it is a conductive layer formed of a conductive paint, but it is usually a layer that functions as an electrode. The conductive coating is not particularly limited, and conventional coatings can be used, and conductive coatings containing conductive fillers and binders are preferred.

In the present invention, the so-called "conductivity" means having less than 1×10 ^-3 Ω. The specific resistance in cm. The specific resistance can be measured with a digital multimeter, and then calculated using the following formula.

Specific resistance (Ω.cm)=R×S/l [R: resistance value measured by a digital multimeter, S: cross-sectional area of the layer formed by conductive paint, l: distance between electrodes]

The aforementioned conductive filler is not particularly limited, and conventional fillers can be used.

The conductive filler contained in the aforementioned conductive paint may be one type, or two or more types that are different in shape, size, material, and the like.

The material of the aforementioned conductive filler is not particularly limited as long as it is conductive, and it can be metals such as copper, silver, gold, tin, bismuth, zinc, indium, nickel, and palladium, and alloys containing these metals. , Carbon black and graphite, especially copper, silver and carbon black.

The conductive filler may also be a filler obtained by plating the metal or alloy or the like on the surface of a certain material.

The shape of the conductive filler is not particularly limited, and may be, for example, a block shape, a spherical shape, a flake shape, a needle shape, a fiber shape, a dendrite shape, or a coil shape.

The median diameter (D50) of the aforementioned conductive filler measured by the laser diffraction scattering method (Microtrac method) can be used to obtain a coating with good paintability, and a layer with good conductivity can be easily obtained. From the point of view of others, it is preferably 5 to 30 μm.

From the point of view that a layer with good conductivity can be easily obtained, the content of the conductive filler is preferably 60% by mass or more, and more preferably 65% by mass or more relative to the solid content of the conductive paint 100% by mass. , Preferably 95% by mass or less, more preferably 93% by mass or less.

Although the aforementioned binder is not particularly limited, it is preferably one that can retain the aforementioned conductive filler.

The binder contained in the aforementioned conductive paint may be one type or two or more types.

The aforementioned binder is not particularly limited, and may be, for example, thermoplastic resins such as polyester resins, acrylic resins, butyral resins, and thermoplastic imine resins; bisphenol A type, bisphenol F type, novolak type, etc. Epoxy compounds such as oxygen resins and liquid epoxy compounds, polyester resins such as unsaturated polyester resins, polyurethane resins, phenol resins such as resol type and novolak type, and thermosetting resins such as imide resins Resins: styrene elastomers, olefin elastomers, polyester elastomers, polyurethane elastomers, polyamide elastomers, silicone elastomers and other elastomers.

From the point of view that the conductive filler can be sufficiently maintained, and a layer with good shape retention and conductivity can be easily obtained, the above-mentioned adhesive is relative to 100 parts by mass of the above-mentioned conductive filler. The content of the agent is preferably 5 parts by mass or more, more preferably 7 parts by mass or more, preferably 35 parts by mass or less, and more preferably 20 parts by mass or less.

From the viewpoint of paintability, etc., the aforementioned conductive paint preferably contains one or more solvents. The solvent is not particularly limited, and may be, for example, methanol, ethanol, isopropanol, and butylcarbitol. Alcohol solvents such as butyl carbitol, butyl cellosolve, propylene glycol monomethyl ether; aromatic solvents such as toluene and xylene, methyl isobutyl ketone, etc. Ketone solvents; ester solvents such as methyl acetate, ethyl acetate, and butyl carbitol acetate.

In addition to the aforementioned components, the aforementioned conductive paint may optionally contain conventional additives within a range that does not impair the effects of the present invention.

Examples of such additives include: saturated fatty acids such as palmitic acid and stearic acid; unsaturated fatty acids such as linolenic acid, linoleic acid, and oleic acid; Metal salts of these acids (examples of metals: sodium and potassium); organic acids with hydroxyl groups such as lactic acid and tartaric acid; organic acids with sulfonic acid groups such as alkyl sulfonic acid series and alkyl benzene sulfonic acid; metal chelate Forming agent; hardener used to harden the hardening resin; dispersant; film forming aid; surface modifier; plasticizer; anti-aging agent; pigment.

Each of these additives may be one type or two or more types.

From the point of view that a sensor with high output voltage can be easily obtained during initial and long-term use, the value of the flexural rigidity of the conductive coating layer is preferably 0.1 GPa or more, and more preferably 0.4 GPa or more , Particularly preferably 0.5 GPa or more, preferably 30 GPa or less, more preferably 20 GPa or less, and particularly preferably 10 GPa or less.

The thickness of the conductive coating film layer is not particularly limited. It may be the same thickness as that of conventional electrodes. However, it is preferable to have a thickness capable of keeping the bending rigidity in the above-mentioned range, so that the desired sensor and the like can be easily manufactured. From a point of view, it is preferably 1 to 1000 μm, and more preferably 1 to 100 μm.

In addition, when the piezoelectric layer is a porous layer and a conductive paint is applied to such a porous layer, a dried or hardened conductive paint may be formed inside the porous layer. However, In this case, the thickness of the aforementioned conductive coating film layer also refers to the thickness from the surface of the porous layer.

<Piezoelectric layer>

The aforementioned piezoelectric layer is not particularly limited, and conventionally known piezoelectric sheets can be used, such as: piezoelectric resin layer; porous layer; made of inorganic pressure such as crystal, barium titanate, lead zirconate titanate, etc. A layer made of electrical materials.

The aforementioned piezoelectric layer may be of a monomorph type, a bimorph type, or a laminated type.

In addition, the shape, size, and the like of the piezoelectric layer are not particularly limited, and can be appropriately selected according to the intended use and the like.

The thickness of the aforementioned piezoelectric layer can be appropriately selected according to the intended use, but is usually 10 μm or more, preferably 50 μm or more, usually 1 mm or less, and preferably 500 μm or less.

As the piezoelectric layer, a porous layer is preferred, and a porous sheet containing a resin component is more preferred. Specific examples of the porous sheet include porous organic polymer sheets, non-woven fabrics or woven fabrics containing organic polymers.

Among them, from the viewpoint of long-term maintenance of durability, deformation performance, etc., non-woven fabrics or woven fabrics containing organic polymers are particularly preferred, and even more preferred are those constructed by attaching organic polymers to insulating non-woven fabrics or woven fabrics. , Non-woven fabrics or woven fabrics composed of fibers containing organic polymers can be more easily obtained not by the expansion and contraction of the piezoelectric layer but by the external pressure to generate electricity, and will show high levels over a long period of time. In terms of output voltage sensors, glass cloth or glass non-woven cloth containing organic polymers is particularly preferred.

From the viewpoint of easily obtaining a piezoelectric layer with high charge retention, etc., the porosity of the porous layer is preferably 0.1% by volume or more, more preferably 1% by volume or more, and even more preferably 2 Volume% or more, preferably 70 volume% or less, more preferably 60 volume% or less, and still more preferably 50 volume% or less.

The porosity can be measured by the method disclosed in the following examples. In addition, the porosity of the porous layer composed of an organic polymer can be calculated by the following method.

Porosity = (true density of organic polymer-apparent density of porous layer) × 100/true density of organic polymer

Among them, the apparent density is a value calculated based on the mass and apparent volume of the porous layer.

Among the aforementioned organic polymers, from the viewpoint of obtaining a piezoelectric layer with high charge retention and good piezoelectric properties, one or more inorganic fillers may be contained within a range that does not impair the effects of the present invention. . From the point of view that a piezoelectric layer with a higher piezoelectric ratio can be obtained, the inorganic The filler is preferably a filler having a higher permittivity than the polymer, for example, an inorganic filler having a relative permittivity ε of 10 to 10,000. 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 aforementioned organic polymer is not particularly limited, and examples include: polytetrafluoroethylene polymer (PTFE), copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether (PFA), copolymerization of tetrafluoroethylene and hexafluoropropylene (FEP), polychlorotrifluoroethylene (PCTFE), copolymer of tetrafluoroethylene and ethylene (ETFE), polyvinylidene fluoride (PVdF), polyvinyl fluoride (PVF), tetrafluoroethylene and hexafluoropropylene and Fluorine-containing resins such as vinylidene fluoride copolymers (THV); polyolefin resins such as polypropylene and polyethylene; polystyrene, poly(meth)acrylate, polyacrylonitrile, polyvinyl chloride, polyvinylidene Vinyl polymers such as vinyl chloride; polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polylactic acid, polyhydroxyalkanoate, polybutylene succinate , Polyethylene succinate, polyethylene succinate adipate (polyethylene succinate adipate) and other polyester-based polymers; nylon 6, nylon 66, nylon 11, nylon 12 and other polyamide-based resins; polyaramide resins Aromatic polyamide resins; imine resins such as polyimine, polyimide imide, polyether imide, bismaleimide, etc.; engineering plastics such as polycarbonate and polycyclic olefin Other thermoplastic resins; unsaturated polyester, vinyl ester resin, diallyl phthalate resin, epoxy resin, phenol resin, polyurethane, silicon resin, alkyd resin, furan resin, dicyclopentadiene Thermosetting resins such as resins, acrylic resins, and allyl carbonate resins; silicone resins.

As the aforementioned organic polymer, the volume resistivity is 1.0×10 ¹³ Ω. cm or more polymers are preferred, for example, polyamide resins, aromatic polyamide resins, polyolefin resins, polyester resins, polyacrylonitrile, phenol resins, fluorine-containing resins, imines Department resin.

Among them, from the viewpoint of good heat resistance and weather resistance, it is preferable to use an organic polymer that does not have a dipole due to a molecular and crystalline structure. Examples of such polymers include polyolefin resins (e.g. polyethylene, polypropylene, ethylene propylene resin), polyester resins (e.g. polyethylene terephthalate), polyurethane resins, and polystyrene resins. , Silicone resin and other non-fluorine resins, as well as polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), etc. Fluorine-containing resin.

Among them, from the standpoint of heat resistance and weather resistance, a polymer that can be used continuously at a high temperature and whose glass transition point is not within the use temperature range of the sensor is preferable. The continuous use temperature can be measured by the continuous use temperature test described in UL746B (UL standard), and it is preferably 50°C or higher, and more preferably 80°C or higher. In addition, from the viewpoint of moisture resistance, a polymer having water repellency is preferred.

As polymers with these characteristics, polyolefin resins and fluorine-containing resins are preferred. In particular, it can be obtained even at high temperatures that the piezoelectric characteristics are not easily degraded and can accurately detect pressure sensors, etc. From a standpoint, fluorine-containing resin is more preferable, and PTFE is particularly preferable. In particular, when PTFE is used as the aforementioned polymer, a sensor having an excellent balance of heat resistance, pressure detection capability, and durability can be obtained.

When the piezoelectric layer is a layer made of a material other than a piezoelectric material, for example, in the case of the porous layer, a layer that has been subjected to polarization treatment is preferable. By applying polarization treatment, charges can be injected into the layer. In the case of a porous layer, the injected charges are concentrated in the pores existing in the porous layer to induce polarization. For the internally polarized layer, a compressive load can be applied in the thickness direction of the layer, and the charge can be taken out through the front and back of the layer. That is, charge movement is generated on the external load (circuit) to obtain electromotive force.

〔Porous organic polymer sheet〕

As the aforementioned porous organic polymer sheet, a sheet composed of an organic polymer capable of holding electric charge is preferable. As such a porous organic polymer sheet, for example, a sheet-like foam composed of an organic polymer, an elongated porous film composed of an organic polymer, a matrix resin (organic polymer) and an electric charge are included. Inducible hollow particles (particles with conductive material attached to at least a part of the surface of the hollow particles) porous organic polymer sheet, formed by removing the phase separation agent dispersed in the organic polymer with an extractant such as supercritical carbon dioxide A sheet formed by the method of pores.

〔Non-woven fabrics or woven fabrics containing organic polymers〕

The non-woven fabric or woven fabric containing an organic polymer, specifically, for example, a non-woven fabric or woven fabric formed by attaching an organic polymer to an insulating non-woven fabric or woven fabric, a non-woven fabric or woven fabric composed of fibers containing an organic polymer, and the like. Among them, from the viewpoint of further exerting the aforementioned effects and the like, it is preferable to attach an organic polymer to an insulating non-woven fabric or woven fabric.

The aforementioned non-woven fabrics can be made by wet papermaking method, water punch method, chemical bond method, thermal bond method, spun bond method, needle punch method Non-woven fabrics made by various manufacturing methods such as stitch-bond methods, but from the viewpoints of heat resistance, mechanical properties, and solvent resistance, it is better to use a hot-melt bonding method using self-melting fibers or Non-woven fabric made by spunbond method.

The fiber (filament) constituting the aforementioned woven fabric may be any of monofilament, multifilament, and staple. The weaving method is also not particularly limited, and examples thereof include plain weave, twill weave, satin weave, double weave, and cylindrical weave. In terms of weaving structure, the weaving yarn structure, yarn count, and yarn density are not particularly limited.

The average fiber diameter of the fibers constituting the aforementioned non-woven fabric or woven fabric is preferably 0.05 μm or more, more preferably 0.1 μm or more, still more preferably 0.3 μm or more, preferably 50 μm or less, and more preferably 20 μm Hereinafter, it is more preferable to be 10 μm or less.

When the average fiber diameter is within the aforementioned range, a non-woven fabric or woven fabric showing high flexibility can be formed, and a sufficient charge-holding space can be formed due to the increased surface area of the fiber, even when a thin non-woven fabric or woven fabric is formed It is preferable to improve the uniformity of fiber distribution.

The average fiber diameter of the fibers constituting the aforementioned non-woven fabric or woven fabric can be adjusted by appropriately selecting the conditions for forming the fibers. For example, when manufacturing by the electrospinning method, there are: Humidity, reducing the nozzle diameter, increasing the applied voltage, or increasing the voltage density can reduce the average fiber diameter of the obtained fiber.

In addition, the aforementioned average fiber diameter system: Observe (magnification: 10000 times) the fiber (group) to be measured with a scanning electron microscope (SEM), randomly select 20 fibers from the obtained SEM image, and measure the fiber diameter of each fiber ( Long diameter), the average value calculated based on the measurement result.

The fiber diameter variation coefficient calculated by the following formula of the fibers constituting the aforementioned non-woven fabric or woven fabric is preferably 0.7 or less, and more preferably 0.01 or more and 0.5 or less. When the fiber diameter variation coefficient is within the aforementioned range, the fiber diameter of the fiber will be uniform, and the non-woven fabric or woven fabric obtained by using the fiber will have a higher porosity, so a non-woven fabric or woven fabric with high charge retention can be obtained. Therefore it is better.

Coefficient of variation of fiber diameter = standard deviation/average fiber diameter (the so-called "standard deviation" refers to the standard deviation of the fiber diameters of the aforementioned 20 fibers.)

The fiber length of the fibers constituting the aforementioned non-woven fabric or woven fabric is preferably 0.1 mm or more, more preferably 0.5 mm or more, still more preferably 1 mm or more, preferably 1000 mm or less, and more preferably 100 mm or less, More preferably, it is 50 mm or less.

The basis weight (weight per unit area) of the aforementioned non-woven fabric and woven fabric is preferably 100 g/m ² or less, more preferably 0.1 to 50 g/m ² , and still more preferably 0.1 to 20 g/m ² .

The aforementioned basis weight tends to increase due to the lengthening of the spinning time and the increase of the number of spinning nozzles.

The aforementioned non-woven fabrics and woven fabrics are made by stacking or woven into sheets of the aforementioned fibers. Such non-woven fabrics and woven fabrics may be composed of a single layer or two or more layers with different materials and fiber diameters. Either.

‧Organic polymer attached to insulating non-woven fabric or woven fabric

The presence of the organic polymer in the non-woven fabric or woven fabric made by attaching the organic polymer to the insulating non-woven fabric (hereinafter referred to as "organic polymer attachment") is not particularly limited, and it may be attached to the non-woven fabric or woven fabric constituting the insulating non-woven fabric. The fibers of the cloth may also be voids existing in the insulating non-woven fabric or woven fabric, but it is preferable to coat the fibers constituting the insulating non-woven fabric or woven fabric.

The aforementioned insulating non-woven fabric or woven fabric may be a non-woven fabric or woven fabric made of an organic material, or a non-woven fabric or a woven fabric made of an inorganic material, but from the viewpoint of further exerting the aforementioned effects, etc., it is preferably made of an inorganic material Non-woven or woven cloth.

Examples of the organic material include the same polymers as the aforementioned organic polymers.

Examples of the inorganic material include ceramic fibers such as glass fiber, rock wool, carbon fiber, alumina fiber, wollastonite, or potassium titanate. Among them, glass fiber and/or ceramic fiber are particularly preferred.

From the viewpoint of charging characteristics, the insulating non-woven fabric or woven fabric may be positively charged or negatively charged.

In addition, the charging tendency of the insulating non-woven fabric or woven fabric and the attached organic polymer may be approximately the same or different, but a combination of materials that are far apart on the charged column is preferred. When the insulating non-woven fabric or woven fabric is made of glass woven fabric, it is easy to obtain a piezoelectric layer that exhibits a high-voltage electric constant and can maintain a high-voltage electric rate, so it is preferable.

The organic polymer attached to the insulating non-woven fabric or woven fabric may be one that is easy to be negatively charged or one that is easy to be positively charged from the viewpoint of charging characteristics. When the insulating non-woven fabric or woven fabric is made of glass fiber, the organic polymer is preferably a resin with a charged column on the negative side compared to the glass fiber, for example, a fluorine-containing resin.

In addition, the organic polymer attached to the aforementioned insulating non-woven fabric or woven fabric is preferably a resin with a high melting temperature and a high thermal decomposition starting temperature from the viewpoint of heat resistance. For example, a fluorine-containing resin, a Imine resins are preferred, and fluorine-containing resins, especially PTFE, are preferred when combined with glass woven fabrics or non-woven fabrics. When such a fluorine-containing resin or imine-based resin is used, the resulting piezoelectric layer has excellent heat resistance and weather resistance, especially the piezoelectric properties at a high temperature of 70°C or higher. good.

The method for producing the aforementioned organic polymer attachment is not particularly limited, but from the viewpoint of ease of production, etc., the insulating non-woven fabric or woven fabric is immersed in an organic polymer (liquid containing the organic polymer), and then The insulating non-woven fabric or woven fabric is taken out and then dried or hardened.

The content of the organic polymer in the aforementioned organic polymer attachment is, from the point of view that it is easier to obtain a sensor that displays a higher output voltage, etc., preferably 10% by mass or more, and more preferably 30% by mass or more , Preferably 90% by mass or less, more preferably 80% by mass or less.

The content can be, for example, the change in mass before and after heating when heated at a temperature above the decomposition start temperature of the organic polymer and below the softening temperature of the material constituting the insulating non-woven fabric or woven fabric in an inert gas atmosphere such as nitrogen And figure it out.

‧Non-woven fabrics or woven fabrics composed of fibers containing organic polymers

The fiber is produced by, for example, electrospinning, melt spinning, melt electrospinning, spunbonding (melt blowing), wet method, and spunlace method, but especially by electrospinning The fiber diameter of the obtained fiber is small, and the non-woven fabric or woven fabric formed with such fibers has a high porosity and a high specific surface area. Therefore, a non-woven fabric or woven fabric with high-voltage electrical properties can be obtained.

When an electrospinning method is used to form a fiber containing an organic polymer, for example, a spinning solution containing the aforementioned organic polymer and an optional solvent is used.

The ratio of the organic polymer contained in the aforementioned spinning solution is, for example, 5% by mass or more, preferably 10% by mass or more, for example, 100% by mass or less, preferably 80% by mass or less, and more preferably 70% by mass. Less than mass%.

The aforementioned polymers may be used singly, or two or more kinds may be used.

The aforementioned solvent is not particularly limited as long as it can dissolve or disperse the aforementioned polymer, and can be, for example, water, dimethylacetamide, dimethylformamide, tetrahydrofuran, methylpyrrolidone, xylene, Acetone, chloroform, ethylbenzene, cyclohexane, benzene, cyclobutylene, methanol, Ethanol, phenol, pyridine, propylene carbonate, acetonitrile, trichloroethane, hexafluoroisopropanol, diethyl ether. One type of these solvents may be used, or two or more types may be used.

The content of the aforementioned solvent in the spinning solution is, for example, 0% by mass or more, preferably 10% by mass or more, more preferably 20% by mass or more, for example, 90% by mass or less, and preferably 80% by mass or less .

In addition to the aforementioned organic polymer, the spinning solution may contain additives such as inorganic fillers, surfactants, dispersants, charge regulators, functional particles, adhesives, viscosity regulators, and fiber forming agents. These additives may be used individually by 1 type, and 2 or more types may also be used.

In the aforementioned spinning solution, if the solubility of the aforementioned organic polymer in the aforementioned solvent is low (for example, when the organic polymer is PTFE and the solvent is water), it is necessary to maintain the fiber shape of the organic polymer during spinning. It seems that it is better to contain one or more fiber forming agents.

As the aforementioned fiber forming agent, an organic polymer having high solubility in a solvent is preferred, and examples thereof include polyethylene oxide, polyethylene glycol, polydextrose, alginic acid, chitosan, starch, Polyvinylpyrrolidone, polyacrylic acid, polymethacrylic acid, polyacrylamide, cellulose, polyvinyl alcohol.

When the aforementioned fiber-forming agent is used, although it depends on the viscosity of the solvent and the solubility in the solvent, the content of the aforementioned fiber-forming agent in the spinning solution is, for example, 0.1% by mass or more, preferably 1% by mass or more, for example, 15% by mass or less, preferably 10% by mass or less.

The aforementioned spinning solution can be produced by mixing the aforementioned organic polymer, solvent, and additives as needed by a conventional method.

When the aforementioned organic polymer is PTFE, preferred examples of the aforementioned spinning solution include the following spinning solution (1).

Spinning solution (1): Contains 30% by mass or more, 70% by mass or less, preferably 35% by mass or more, more preferably 60% by mass or less PTFE, and contains 0.1% by mass or more and 10% by mass or less. Preferably, 1% by mass or more, and more preferably 7% by mass or less of fiber forming agent, and spinning solution containing 100% by mass of the remaining solvent in total

The applied voltage during electrospinning is preferably 1kV or more, more preferably 5kV or more, still more preferably 10kV or more, more preferably 100kV or less, more preferably 50kV or less, and still more preferably Below 40kV.

The tip diameter (outer diameter) of the spinning nozzle used in electrospinning is preferably 0.1 mm or more, more preferably 0.2 mm or more, more preferably 2.0 mm or less, and more preferably 1.6 mm or less.

More specifically, for example, when the aforementioned spinning solution (1) is used, the aforementioned applied voltage is preferably 10 to 50 kV, more preferably 10 to 40 kV, and the tip diameter (outer diameter) of the aforementioned spinning nozzle is preferably It is 0.3 to 1.6mm.

When using the aforementioned fibers to form a nonwoven fabric, specifically, for example, the steps of manufacturing the aforementioned fibers by electrospinning and the step of stacking the aforementioned fibers into sheets to form a non-woven fabric can be performed at the same time, or the aforementioned manufacturing process can be performed at the same time. After the step of fiber, the step of forming a non-woven fabric by stacking the aforementioned fibers into a sheet by a wet method or the like is performed.

The method of forming a non-woven fabric by the aforementioned wet method includes, for example, a method of using an aqueous dispersion containing the aforementioned fibers to accumulate (accumulate) the aforementioned fibers on a mesh, for example, and forming (paper making) into a sheet. .

The amount of fiber used in this wet method is preferably 0.1 to 10% by mass, and more preferably 0.1 to 5% by mass relative to the total amount of the aforementioned aqueous dispersion. When the fibers are used in this range, water can be efficiently used in the step of accumulating the fibers, and the dispersion state of the fibers will be improved, and a uniform wet non-woven fabric can be obtained.

In the aforementioned aqueous dispersion, in order to achieve a good dispersion state, a dispersant or oil composed of a cationic, anionic, non-ionic surfactant, etc., and a defoamer to suppress the generation of bubbles can be added. Or more than 2 kinds.

When the aforementioned fiber is used to form a woven fabric, it can be produced by a method including a step of manufacturing the aforementioned fiber and a step of weaving the obtained fiber into a sheet to form a woven fabric.

The method of weaving fibers into a sheet can be a conventional weaving method, such as: water jet loom, air jet loom, rapier loom, etc.

When the aforementioned organic polymer is PTFE, it is preferable to perform a heat treatment after forming a non-woven fabric or a woven fabric. The heat treatment is performed by subjecting the obtained non-woven fabric or woven fabric to a heat treatment generally at 200 to 390°C for 30 to 300 minutes. By this heat treatment, the aforementioned solvent, fiber forming agent, etc. remaining on the non-woven fabric or woven fabric can be removed.

For example, a case where the method of manufacturing the aforementioned nonwoven fabric includes a step of manufacturing a fiber made of PTFE by an electrospinning method will be specifically described. The manufacturing method of the non-woven fabric composed of PTFE fiber can adopt the conventional manufacturing method, for example, the following method described in JP 2012-515850 A, that is, a method including the following steps:

The step of providing a spinning solution containing PTFE, a fiber forming agent and a solvent, and having a viscosity of at least 50,000 cP;

The step of spinning the spinning solution using a nozzle and making it fiberized by electrostatic traction;

The step of collecting the aforementioned fibers on a collector (for example: a take-up reel) to form a precursor;

The step of baking the precursor to remove the solvent and the fiber forming agent to form a non-woven fabric made of PTFE fibers.

"Manufacturing Method of Piezoelectric Sensor"

The manufacturing method of the piezoelectric sensor of one embodiment of the present invention (hereinafter referred to as "the manufacturing method") is a piezoelectric sensor (compared to Preferably, the manufacturing method of the aforementioned sensor) includes the steps of applying the conductive paint to the piezoelectric layer, and then drying or hardening the applied paint.

The method of applying conductive paint is not particularly limited, and conventional methods can be used without limitation. Examples include: airless spray, air spray, brush coating, roller coating, etc. , The method of immersing the piezoelectric layer in conductive paint.

In this coating, it is preferable to perform coating so that the thickness of the piezoelectric layer to be formed is within the aforementioned range.

The conditions for drying or hardening the aforementioned paint are not particularly limited, as long as they are appropriately selected according to the binder and solvent used, and it can be dried and/or hardened at room temperature, or it can be heated under heating. Dry and/or harden.

In addition, the aforementioned drying or curing can also be carried out under reduced pressure, or under an inert gas atmosphere such as a nitrogen atmosphere, if necessary.

When laminating the aforementioned metal layer and piezoelectric, an adhesive may be used as needed, and it is also possible to simply bring the metal foil or the like into contact with the piezoelectric sheet or the like. In the latter case, pressure can also be applied after the contact as described above.

Before laminating the metal layer and the piezoelectric layer, or before coating the conductive paint, it is preferable to perform surface treatment on the surface of the metal layer and the piezoelectric layer by a conventional method such as plasma treatment or corona treatment.

If the piezoelectric layer is a layer made of a material other than a piezoelectric material, for example, in the case of the porous layer, it is preferable to subject the piezoelectric layer to polarization treatment. By applying polarization treatment, charges can be injected into the layer.

The method of the aforementioned polarization treatment can be a conventional method, and is not particularly limited. Examples thereof include voltage application treatment such as DC voltage application treatment and AC voltage application treatment, and corona discharge treatment.

For example, the corona discharge treatment can be performed using a device composed of a commercially available high-voltage power supply and electrodes.

The discharge conditions may be appropriately selected according to the material and thickness of the piezoelectric layer used. For example, when the piezoelectric layer is a porous layer made of PTFE, the preferable conditions include: The voltage is -0.1 to -100kV, more preferably -1 to -20kV, the current is 0.1mA or more, 100mA or less, more preferably 1mA or more, 80mA or less, the distance between electrodes is 0.1cm or more, 100cm or less, more preferably Those are 1cm or more, 10cm or less, and the applied voltage is 0.01MV/m or more, 10.0MV/m or less, more preferably 0.5MV/m or more, 2.0MV/m or less.

The aforementioned polarization treatment may be a polarization treatment performed on a piezoelectric layer alone such as a piezoelectric sheet, but it is preferably after the formation of the aforementioned conductive coating film, after the piezoelectric layer and the metal are laminated, and after the formation After a laminate including a metal layer, a piezoelectric layer, and a conductive coating layer in this order, and after forming the laminate when a conventionally known laminate such as a porous layer and an insulating layer is used as the piezoelectric layer, etc. Polarization treatment.

This can be thought to be because the layer laminated with the piezoelectric can be used to prevent the electric charge held in the piezoelectric layer from being attenuated after being electrically connected to the external environment by the polarization treatment, and a higher sensitivity of the piezoelectric inductance measurement can be obtained. The reason for the device may be thought to be because there is a tendency to form a new interface capable of holding charge between the piezoelectric layer and the layer laminated with the piezoelectric, so that the resulting piezoelectric sensor The piezoelectric ratio of the piezoelectric layer is increased.

[Example]

Next, examples are presented to explain in more detail an embodiment of the present invention, but the present invention is not limited by these examples.

[Example 1]

Coat Polycalm PCS-1201S (contains conductive filler and adhesive) manufactured by Plascoat Co., Ltd. on a 9 cm square area of the center of one side of the following piezoelectric sheet of 10 cm square. It hardens to form a conductive coating film (thickness: 10μm), which is used as a signal electrode.

The aforementioned piezoelectric sheet was produced as follows.

Bundle glass fibers with a single fiber diameter of 5 to 8 μm and a fiber diameter variation coefficient of 0.3 to form a fiber bundle (fiber bundle diameter (long diameter): 15 μm), and use the obtained fiber bundle for plain weaving. Into glass woven fabric. This glass woven fabric was immersed in a PTFE dispersion liquid, and PTFE particles were impregnated therein to produce a piezoelectric sheet (thickness: 100 μm).

The basis weight of the obtained piezoelectric sheet was 1.2 g/m ² .

A test piece was cut from the obtained piezoelectric sheet, and heated at 400°C for 30 minutes in a nitrogen atmosphere. The mass of the glass and the PTFE were calculated from the mass changes before and after the heating, and the PTFE content ratio. The PTFE content ratio is 35% by mass.

In addition, from the aforementioned mass ratio of PTFE and glass and the measured value of the mass of the test piece, the theoretical volume of the test piece assuming no voids is calculated, and the measured volume of the test piece is calculated by measuring the size of the test piece, using the following formula The porosity of the obtained piezoelectric sheet is calculated from the difference between the theoretical volume and the measured volume. The porosity is 34% by volume.

Porosity (volume%)=(1-(theoretical volume/measured volume))×100

On the side of the piezoelectric sheet opposite to the conductive coating film, a 9cm square aluminum foil (thickness: 18μm) was set as a ground electrode to form a piezoelectric sensor.

Using a corona discharge device manufactured by Kasuga Electric Co., Ltd., the distance between the electrodes is 12.5mm, the voltage between the electrodes is -15kV, at room temperature for 3 minutes (under the condition that no overcurrent occurs), and the obtained The piezoelectric sensor performs corona discharge to complete the polarization treatment of the piezoelectric sensor.

In order to extract electrical signals from the piezoelectric sensor to the polarized piezoelectric sensor, silver paste is used to electrically connect the signal electrode with the core wire of the coaxial cable, and silver paste is used for the ground electrode and the braided wire of the coaxial cable Electric connection.

The bending rigidity of the signal electrode and the ground electrode of the obtained piezoelectric sheet was measured in the following manner. The bending rigidity of the signal pole is 2GPa, and the bending rigidity of the grounding pole is 70GPa.

<Bending rigidity>

The bending stiffness is defined as the product of the Young's coefficient of the material and the second moment of section. The second moment of section is shown by W×D ³ /12, and W and D are the width and thickness of the material, respectively.

The Young’s coefficient of the signal pole is measured according to the following method: Polycalm PCS-1201S is coated on a glass plate, cured at 80°C for 30 minutes to harden, and then peeled from the glass plate to obtain a coating film with a thickness of 10μm , And then use the resulting coating film to perform a static test in accordance with JIS R 1602 (3-point bending method) to obtain the Young's coefficient.

The Young's coefficient of the ground electrode is measured by using the aluminum foil before lamination as described above, and the static Young's coefficient is measured in accordance with JIS Z 2280 (3-point bending method).

The entire piezoelectric sensor connected to the aforementioned coaxial cable was sealed with PET tape, and then conductive tape was layered on the outer two areas as an electromagnetic shielding layer. Then, silver glue is used to electrically connect the electromagnetic shielding layer and the braided wire of the aforementioned coaxial cable. Then, the obtained laminate was sealed with a PET tape to produce a sensor for evaluation.

<The initial performance evaluation of the sensor for pressing>

In order to evaluate the initial performance of the evaluation sensor, the finished evaluation sensor is placed on an insulating level table with the signal pole on the lower side, and the coaxial cable is connected to the oscilloscope according to JIS B 9717 -1 to measure the output voltage. At room temperature, for as above The upper center of the placed evaluation sensor was pressed from the vertical direction with a stainless steel indenter of ψ 80 mm at a speed of 2 mm/s, and the output voltage during pressing was measured. The results are shown in Table 1.

<Evaluation of the durability of the sensor to withstand repeated pressing>

In order to evaluate the durability of the sensor for evaluation, the same method as the previous method is used at room temperature with a ψ80mm stainless steel indenter at a speed of 500mm/s from an angle of 14° with respect to the vertical direction. Ground pressing the upper center of the evaluation sensor connected to the oscilloscope, specifically, measuring each output voltage when pressing 10,000 times, 100,000 times, or 1,000,000 times. The results are shown in Table 1.

[Comparative Example 1]

Except that the same aluminum foil as the ground electrode was used instead of the conductive coating film as the signal electrode, a sensor for evaluation was produced in the same manner as in Example 1, and the performance of the sensor was performed in the same manner as in Example 1. Evaluation. The results are shown in Table 1.

[Example 2]

Except that a 9 cm square copper foil (thickness: 35 μm) was used instead of the ground electrode used in Example 1 as the ground electrode, as in Example 1, the durability of the sensor against repeated pressing was evaluated. If the output voltage is 1500mV or more when pressed 1000 times, it is evaluated as AA, if it is 1000mV or more and less than 1500mV, it is evaluated as BB, if it is 300mV or more and less than 1000mV, it is evaluated as CC, and if it is less than 300mV. For DD. The results are shown in Table 2.

In addition, the bending rigidity of the ground electrode measured in the same manner as in Example 1 was 129 GPa.

[Example 3]

Except that a 9 cm square nickel foil (thickness: 30 μm) was used instead of the ground electrode used in Example 2 as the ground electrode, as in Example 2, the durability of the sensor against repeated pressing was evaluated. The results are shown in Table 2.

In addition, the bending rigidity of the ground electrode measured in the same manner as in Example 1 was 198 GPa.

[Comparative Example 2]

Except that a 9 cm square copper foil (thickness: 35 μm) was used instead of the signal electrode used in Example 3 as the signal electrode, as in Example 3, the durability of the sensor against repeated pressing was evaluated. The results are shown in Table 2.

In addition, the bending rigidity of the signal pole obtained by measuring in the same manner as in Example 1 was 129 GPa. The Young's coefficient of the signal pole at this time was measured using the copper foil before lamination, and the static Young's coefficient was measured in accordance with JIS Z 2280 (three-point bending method).

Claims (8)

A piezoelectric sensor, which includes a metal layer, a piezoelectric layer, and a conductive coating layer in sequence, in which, The ratio of the bending rigidity of the aforementioned metal layer to the bending rigidity of the aforementioned conductive coating film layer is 10-100. Such as the piezoelectric sensor described in item 1 of the scope of patent application, in which: The aforementioned conductive coating layer is a layer containing a conductive filler and a binder. Such as the piezoelectric sensor described in item 1 or 2 of the scope of patent application, in which, The aforementioned piezoelectric layer is a non-woven fabric or woven fabric containing an organic polymer, and the organic polymer does not have a dipole due to a molecular and crystalline structure. Such as the piezoelectric sensor described in item 3 of the scope of patent application, in which, The aforementioned organic polymer is polytetrafluoroethylene. Such as the piezoelectric sensor described in item 3 of the scope of patent application, in which, The average fiber diameter of the fibers constituting the aforementioned non-woven fabric or woven fabric is 0.05 to 50 μm. Such as the piezoelectric sensor described in item 3 of the scope of patent application, in which: The fiber diameter variation coefficient of the fibers constituting the aforementioned non-woven fabric or woven fabric is 0.7 or less. Such as the piezoelectric sensor described in item 1 or 2 of the scope of patent application, in which: The aforementioned piezoelectric layer has a porosity of 0.1 to 70% by volume. A manufacturing method of a piezoelectric sensor comprising a metal layer, a piezoelectric layer and a conductive coating layer in sequence, which comprises: The step of coating a composition containing conductive filler and adhesive on the piezoelectric layer, and then drying or hardening the coated composition.