JPWO2015167014A1 - Sound wave detection element - Google Patents

Abstract

An acoustic wave detecting element comprising a porous resin body made of a resin not having a dipole due to a molecule and a crystal structure, and a pressure vessel.

Description

  The present invention relates to a sound wave detection element.

  Since sound waves, especially ultrasonic waves, can be examined non-destructively and harmlessly, etc., they can be used in various fields such as inspection of structural defects, diagnosis of human and animal diseases, sounding instruments, and detectors. Applied.

  As an element for detecting such a sound wave, for example, Patent Document 1 discloses an ultrasonic transducer in which a piezoelectric element is incorporated in a case, and Patent Document 2 discloses a piezoelectric element bonded to the case. An ultrasonic transducer having a body is disclosed.

JP-A-11-295281 JP 2006-166183 A

However, the sound wave detection elements described in the above-mentioned patent documents have problems in terms of durability such as long-term characteristic maintenance and heat resistance, and there is room for further improvement.
This invention is made | formed in view of such a problem, and it aims at providing the sound wave detection element excellent in sound wave detection capability and durability.

Under such circumstances, the present inventors have intensively studied to solve the above problems, and as a result, have a porous resin body made of a resin that does not have a dipole attributed to a molecule and a crystal structure, and a pressure vessel. According to the sound wave detection element, the inventors have found that the above object can be achieved, and have completed the present invention.
The configuration of the present invention is as follows.

[1] A sound wave detecting element having a porous resin body made of a resin having no dipole due to a molecule and a crystal structure and a pressure vessel.
[2] The sound wave detecting element according to [1], wherein the porosity of the porous resin body is 60% or more.

  [3] The sound wave detecting element according to [1] or [2], wherein the resin is polytetrafluoroethylene.

[4] The acoustic wave detection element according to any one of [1] to [3], wherein the porous resin body includes a nonwoven fabric or a woven fabric formed from fibers made of resin.
[5] The sound wave detecting element according to [4], wherein an average fiber diameter of the fibers is 0.05 to 50 μm.

  [6] The sound wave detecting element according to any one of [1] to [5], wherein the porous resin body is subjected to polarization treatment.

[7] The sound wave detecting element according to any one of [1] to [6], wherein the sound pressure transmittance of the pressure vessel is 20% or more.
[8] The sound wave detecting element according to any one of [1] to [7], wherein the pressure vessel has a tensile strength of 50 to 2000 MPa.

  [9] The sound wave detecting element according to any one of [1] to [8], wherein the porous resin body is accommodated in the pressure-resistant container.

  ADVANTAGE OF THE INVENTION According to this invention, the sound wave detection element excellent in sound wave detection capability and durability can be provided.

≪Sound wave detection element≫
The acoustic wave detecting element of the present invention includes a porous resin body made of a resin that does not have a dipole attributed to a molecule and a crystal structure, and a pressure vessel. For this reason, the sound wave detection element of this invention is excellent in sound wave detection ability and durability.
The sound wave detection element of the present invention can be used in various fields such as inspection of defects in structures, diagnosis of human and animal diseases, sounding instruments or detectors, and is particularly high in an environment where the temperature is higher than room temperature. It can be suitably used for applications where it is desired to detect sound waves in an environment where pressure is applied (eg, an environment where the pressure is 1 MPa or more).
The sound wave detecting element of the present invention is suitably used as an ultrasonic wave detecting element.

  The structure of the acoustic wave detection element of the present invention is not particularly limited as long as it has the porous resin body and the pressure vessel, but is preferably an element in which the porous resin body is accommodated in the pressure vessel.

  In the acoustic wave detection element of the present invention, there may be a conventionally known layer other than the porous resin body and the pressure vessel, and this layer may be present inside the pressure vessel or outside. May be present. Examples of such conventionally known layers include an adhesive layer for bonding the porous resin body and the pressure resistant container, an electrode layer, and an insulating layer.

  The conventionally known layer is preferably a layer covering at least a part of the surface of the porous resin body from the viewpoint of obtaining a sound wave detecting element including a porous resin body that maintains a high piezoelectricity.

<Porous resin body>
In the sound wave detection element of the present invention, a porous resin body made of a resin that does not have a dipole due to a molecule and a crystal structure is used as a piezoelectric material, and plays a role of detecting sound waves by converting sound waves into electric power. .
The porous resin body has high charge responsiveness to minute external forces, high sound wave detection ability, and can retain electric charge even in a high temperature environment. It is possible to obtain a sound wave detecting element that is highly flexible, excellent in impact resistance and heat resistance, and lightweight. Furthermore, since the porous resin body can be easily formed into an arbitrary shape such as a thin film or a large area, a sound wave detecting element having an arbitrary shape can be manufactured according to a desired application.

  The porous resin body is preferably a structure made of a resin capable of holding an electric charge, and more preferably a structure made of a resin having heat resistance.

  The resin having no dipole due to the molecule and crystal structure is not particularly limited as long as the molecule and crystal structure are not polar resins, but polyolefin resin (polyethylene, polypropylene, ethylene propylene resin, etc.), polyester resin Non-fluorinated resins such as resins (polyethylene terephthalate, etc.), polyurethane resins, polystyrene resins, silicone resins, etc., and polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers (PFA), tetrafluoro Examples thereof include fluorine resins such as ethylene-hexafluoropropylene copolymer (FEP).

Among these, from the viewpoints of heat resistance, weather resistance, and the like, a resin that has a high continuously usable temperature and does not have a glass transition point in the operating temperature range of the acoustic wave detection element is preferable. The continuous useable temperature can be measured by a continuous use temperature test described in UL746B (UL standard), preferably 50 ° C or higher, more preferably 100 ° C or higher, and further preferably 200 ° C or higher. . From the viewpoint of moisture resistance, a resin exhibiting water repellency is preferable.
As the resin having these characteristics, for example, polyolefin resin and fluorine resin are preferable, fluorine resin is more preferable, and PTFE is particularly preferable.

  In particular, when PTFE is used as the resin, it is possible to obtain a sound wave detection element having a good balance between heat resistance, sound wave detection ability, and durability. Since the structure can be maintained, it can be suitably used as a sound wave detection element for inspecting high-temperature members such as underground excavation and oil plant piping under these circumstances.

The porous resin body may contain a conventionally known additive in addition to the resin as long as the effects of the present invention are not impaired.
For example, as the porous resin body, from the viewpoint that a high piezoelectric constant can be maintained for a long period of time, matrix resin and charge-induced hollow particles (particles in which a conductive substance is attached to at least a part of the surface of the hollow particles) The structure containing these may be sufficient.

The initial value of the porous resin body of the piezoelectric constant d ₃₃ (just created the porous resin body) is preferably 110pC / N or more, more preferably about 115~400pC / N, creating a porous resin body Then, the piezoelectric constant d ₃₃ after 5 days is preferably 60 pC / N or more, more preferably 70 pC / N or more, and the piezoelectric constant d ₃₃ after 25 days is preferably 50 pC / N or more.
A porous resin body having a piezoelectric rate in the above range can be suitably used as a piezoelectric material.
The piezoelectric constant is constant AC acceleration α (frequency: 90 to 300 Hz, size: 2 to 10 m / s ² ) in the thickness direction of the porous resin body in a room temperature (20 ° C.) atmosphere and a humidity of 20%. ) And measuring the response charge at that time.

The porous resin body has a porosity calculated by the following formula of preferably 60% or more, more preferably 80 to 99%. A porous resin body having a porosity in the above range is preferable because of its high charge retention amount.
Porosity = (true resin density−apparent density) × 100 / true resin density Note that the apparent density uses a value calculated using the weight of the porous resin body and the apparent volume.

The shape of the porous resin body may be appropriately selected according to the application to be used, but is preferably a sheet from the viewpoint of ease of production, sound wave detectability, and the like.
When the porous resin body is in the form of a sheet, the thickness is not particularly limited, but is, for example, 10 μm to 1 mm, and preferably 50 μm to 500 μm.

  The porous resin body can be obtained by various conventionally known methods. For example, a method of forming pores using the phase change of the solution containing the resin (phase separation method), a method of mixing and dispersing additives for pore formation in the resin and removing them after molding (extraction) Method), molding the resin, and then chemically cutting the bond of a part of the molded body, or conversely performing a binding reaction (chemical treatment method), stretching the resin, A method of forming micropores in the microfibril structure part, a method of mixing and dispersing additives and forming pores during stretching (stretching method), and a method of forming pores by irradiating neutron beams, lasers, etc. ( Irradiation etching method), a method of forming a porous body by fusing resin fine pieces by heating or the like (fusion method), a method of forming pores using a foaming agent (foaming method), Method to form pores by combining (composite method), dry spinning, wet spinning, dry Wherein spinning, melt spinning, to form a fiber (fiber) from the resin by electrospinning like, a method of forming a woven or nonwoven fabric using the fiber and the like.

  The porous resin body is preferably a structure including a nonwoven fabric or a woven fabric formed from fibers made of resin from the viewpoint that durability and deformation performance can be maintained over a long period of time. The structure may include the non-woven fabric or woven fabric, or may be a structure made of only the non-woven fabric or woven fabric, or a laminate in which a conventionally known layer is laminated on the surface of the non-woven fabric or woven fabric. Also good.

  The average fiber diameter of the fiber is preferably 0.05 to 50 μm, more preferably 0.1 to 20 μm, and still more preferably 0.5 μm to 5 μm. A porous resin body containing fibers having an average fiber diameter within the above range can form a sufficient space to retain electric charge by increasing the fiber surface area, and increase the fiber distribution uniformity even when it is made into a thin film. It is preferable in that it can be produced.

  The average fiber diameter can be adjusted by appropriately selecting the conditions for forming the fiber.For example, when the fiber is formed by electrospinning, the humidity is reduced during electrospinning, and the nozzle diameter is adjusted. There is a tendency that the average fiber diameter of the obtained fiber can be reduced by decreasing the voltage, increasing the applied voltage, or increasing the voltage density.

  The average fiber diameter was determined by observing the fiber (group) to be measured with a scanning electron microscope (SEM) (magnification: 10000 times), and randomly selecting 20 fibers from the obtained SEM image. The fiber diameter (major diameter) of each fiber is measured, and is an average value calculated based on the measurement result.

The fiber diameter variation coefficient calculated by the following formula 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 has a uniform fiber diameter, and the nonwoven fabric obtained using the fiber has a higher porosity. Since it is obtained, it is preferable.
Fiber diameter variation coefficient = standard deviation / average fiber diameter (“standard deviation” is the standard deviation of the fiber diameters of the 20 fibers)

  The fiber length of the fiber is preferably 0.1 to 1000 mm, more preferably 0.5 to 100 mm, and still more preferably 1 to 50 mm.

The method for forming the fiber is not particularly limited, but the fiber obtained by the electrospinning method has a small fiber diameter, and the nonwoven fabric obtained by using the fiber has a high hollow ratio and a high specific surface area. From the viewpoint of obtaining a porous resin body having piezoelectric characteristics, the electrospinning method is preferable.
A porous resin body can be produced by accumulating the obtained fibers into a nonwoven fabric or weaving them into a woven fabric and molding them.

[Electrospinning method]
When forming a fiber made of a resin using the electrospinning method, for example, a spinning solution containing the resin and, if necessary, a solvent is used.

  The ratio of the resin contained in the spinning solution is, for example, 5 to 100% by weight, preferably 5 to 80% by weight, and more preferably 10 to 70% by weight.

  The solvent is not particularly limited as long as it can dissolve or disperse the resin. For example, water, dimethylacetamide, dimethylformamide, tetrahydrofuran, methylpyrrolidone, xylene, acetone, chloroform, ethylbenzene, cyclohexane, benzene, sulfolane. , Methanol, ethanol, phenol, pyridine, propylene carbonate, acetonitrile, trichloroethane, hexafluoroisopropanol, and diethyl ether. These solvents may be used alone or in combination of two or more.

  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 25 to 80% by weight.

  In addition to the resin and the solvent, the spinning solution may further contain additives such as a surfactant, a dispersant, a charge adjusting agent, functional particles, an adhesive, a viscosity adjusting agent, and a fiber forming agent. When the spinning solution contains a resin having low solubility in a solvent and the solvent (for example, when the resin is PTFE and the solvent is water), fiber formation is further performed from the viewpoint of forming the resin into a fiber shape during spinning. It is preferable that an agent is included.

  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, Examples thereof include cellulose and polyvinyl alcohol.

  The amount used when the fiber forming agent is used depends on the viscosity of the solvent and the solubility of the resin in the solvent, but is, for example, 0.1 to 15% by weight, preferably 1 to 10% by weight in the spinning solution. .

  The spinning solution can be produced by mixing the resin and, if necessary, a solvent and an additive by a conventionally known method.

Preferable examples of the spinning solution include the following spinning solution (1).
Spinning liquid (1): 30 to 70% by weight, preferably 35 to 60% by weight of PTFE, 0.1 to 10% by weight, preferably 1 to 7% by weight, and a total of 100% by weight. Spinning solution containing solvent

  The applied voltage when performing electrospinning is preferably 1 to 100 kV, more preferably 5 to 50 kV, and still more preferably 10 to 40 kV.

  The tip diameter (outer diameter) of the spinning nozzle used for electrospinning is preferably 0.1 to 2.0 mm, more preferably 0.2 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 0.3 to 1.6 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;
Firing the precursor to remove the solvent and the fiber former to form PTFE fibers.

[Production method of non-woven fabric or woven fabric]
In order to form a nonwoven fabric using the fiber, the step of forming the fiber and the step of collecting the obtained fibers into a sheet to form the nonwoven fabric may be performed separately or simultaneously. (In other words, a nonwoven fabric may be formed by collecting fibers while collecting fibers). Specifically, for example, a step of forming a fiber by using an electrospinning method and a step of collecting the obtained fibers into a sheet to form a nonwoven fabric may be simultaneously performed, or a step of forming a fiber. After performing, you may perform the process of accumulating the fiber obtained by the wet method in a sheet form, and forming a nonwoven fabric.

  Examples of a method for forming a nonwoven fabric by the wet method include a method of forming (paper making) a sheet by depositing (accumulating) the fibers on a mesh using an aqueous dispersion containing the fibers. .

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

  In order to improve the dispersion state, the aqueous dispersion is added with a dispersant or an oil agent composed of a cationic, anionic, or nonionic surfactant, or an antifoaming agent that suppresses the generation of bubbles. May be.

The woven fabric formed from the fiber can be manufactured by a method including a step of forming a fiber and a step of weaving the obtained fiber into a sheet to form a woven fabric.
As a method of weaving the fiber into a sheet, a conventionally known weaving method can be used, and methods such as a water jet room, an air jet room, and a rapier room can be used.

Basis weight of the nonwoven fabric and woven fabric, preferably 100 g / m ² or less, more preferably 0.1 to 50 g / m ^2, more preferably from 0.1 to 20 g / m ^2.
The thickness of the nonwoven fabric and the woven fabric is usually 10 μm to 1 mm, preferably 50 μm to 500 μm.
The basis weight and thickness tend to increase by increasing the spinning time or increasing the number of spinning nozzles.

  The non-woven fabric and woven fabric are obtained by accumulating or weaving the fibers in a sheet shape. Such non-woven fabric and woven fabric are composed of a single layer, or composed of two or more layers having different materials and fiber diameters. Any of these may be used.

[Polarization treatment]
The porous resin body is preferably subjected to polarization treatment from the viewpoint that a porous resin body having a piezoelectric constant d ₃₃ in the above range can be obtained.
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.

For example, the corona discharge treatment can be performed using a commercially available device composed of a high voltage power source and electrodes.
The discharge conditions may be appropriately selected according to the porous resin body to be used. As preferable conditions, the voltage of the high voltage power source is −0.1 to −100 kV, more preferably −1 to −20 kV, and the current is set to 0.1. 1 to 100 mA, more preferably 1 to 80 mA, the interelectrode distance is 0.1 to 100 cm, more preferably 1 to 10 cm, and the applied voltage is 0.01 to 10.0 MV / m, more preferably 0.5 to 2. A condition of 0 MV / m is mentioned.

  In the polarization treatment, the porous resin body alone is usually polarized. However, depending on the pressure vessel used, the polarization treatment may be performed after the porous resin body is accommodated in the vessel.

<Pressure vessel>
The pressure vessel is not particularly limited as long as it is a vessel that blocks external force other than sound waves applied to the porous resin body.
The external force refers to a force (excluding sound waves) applied to the element from the outside of the sound wave detecting element of the present invention, such as pressure or impact.

The sound wave transmittance of the pressure vessel is preferably 20% or more, more preferably 30% or more.
When the sound wave transmittance is in the above range, even when the sound wave detecting element is an element in which the porous resin body is accommodated in the pressure resistant container, the sound wave is not easily absorbed by the pressure resistant container part, and the sound wave is generated by the porous resin body part. Since most of them can be detected, a high-performance acoustic wave detection element is preferable.
The sound wave transmittance can be measured according to JIS A 1405-1.

The tensile strength of the pressure vessel is not particularly limited, and the vessel is preferably strong enough to block external force (pressure) other than sound waves applied to the porous resin body, preferably 50 to 2000 MPa, more Preferably it is 200-2000 MPa.
By using a pressure vessel with a tensile strength in the above range, external forces other than sound waves acting on the porous resin body can be effectively blocked, and external forces (noise) other than sound waves can be detected even in a high static pressure environment. It is possible to obtain a highly sensitive and highly durable sound wave detecting element.
The tensile strength can be measured according to ISO 527-1 (JIS K 7161-7165).

  The size and thickness of the pressure vessel are not particularly limited, and are preferably such size and thickness that the tensile strength falls within the above range, and may be appropriately selected according to the application in which the sound wave detection element of the present invention is used. .

The pressure vessel is not particularly limited, and is preferably a vessel made of a material whose sound transmittance and tensile strength are within the above ranges, and has high electrical insulation (electric resistivity is 1 × 10 ¹² Ω · cm). As described above, the container made of the material also serves to prevent the electric charge held in the porous resin body from being electrically connected to the external environment and attenuated, thereby obtaining a highly sensitive acoustic wave detection element. It is preferable from the viewpoint of being able to

  The pressure vessel may be appropriately selected according to the application in which the acoustic wave detection element of the present invention is used, and examples include containers made of metal materials, inorganic materials such as ceramics and glass, but organic materials such as resins, A container made of a composite material of an inorganic material and an organic material may be used. From the viewpoint of strength and electrical resistivity, a container made of a composite material of inorganic fibers (for example, glass fibers) and a resin material is preferable.

From the viewpoint of reducing reflection of sound waves at the interface with the porous resin body, it is preferable that the acoustic impedance of the material constituting the pressure-resistant container is close to the acoustic impedance of the material constituting the porous resin body. Acoustic impedance of the material of the pressure vessel, ^{usually, 1 × 10 6 ~20 × 10} 6 is preferably ^{kg / m 2 · s, 1} × 10 6 ~10 × 10 6 kg / m 2 · s It is more preferable that it is 1 × 10 ⁶ to 4 × 10 ⁶ kg / m ² · s.

The shape of the pressure vessel is not particularly limited as long as it has an accommodating space inside, but preferably has a space in which the porous resin body can be accommodated. Examples of the shape of the pressure vessel include a polyhedron such as a cube and a rectangular parallelepiped, a sphere, a cylinder, a cone, and the like.
In addition, the pressure vessel may be a partially opened vessel, but is preferably a sealed vessel from the viewpoint of efficiently blocking external force other than sound waves applied to the porous resin body.

  As the pressure vessel, a commercially available product may be used, or a product manufactured by a conventionally known method may be used.

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

[Example 1]
A sheet-like non-woven fabric (thickness 0.06 mm, pores) formed from PTFE fibers as a porous resin body by accumulating PTFE fibers in a sheet form by the electrospinning method described in JP-T-2012-515850 95% in average fiber diameter of 900 nm), and PFA sheet (thickness: 0.025 mm, manufactured by Daikin Industries, Ltd., NEOFLON PFA) as an insulating layer was laminated on the upper and lower surfaces of the nonwoven fabric and heated at 300 ° C. for 60 minutes. A laminated sheet having an insulating layer formed on the front and back surfaces of the porous resin body was produced by pressure bonding. After this laminated sheet was polarized by -15 kV corona discharge irradiation, electrodes were formed by vapor deposition on both sides (on the insulating layer) of the obtained laminated sheet, and lead wires were drawn out to produce an organic piezoelectric element.
This organic piezoelectric element was affixed to the inner surface of a pressure-resistant container (glass fiber reinforced plastic, thickness 2 mm) via a double-sided tape (manufactured by Sumitomo 3M Limited, FPR-12) to produce a sound wave detection element.
When this sound wave detecting element was irradiated with a 10 kHz sound wave from the outside of the pressure vessel toward the pressure vessel, a voltage was generated and the generated voltage was detected. That is, sound waves could be detected by the obtained sound wave detecting element.

Claims (9)

  An acoustic wave detecting element comprising a porous resin body made of a resin not having a dipole due to a molecule and a crystal structure, and a pressure vessel.   The acoustic wave detection element according to claim 1, wherein a porosity of the porous resin body is 60% or more.   The acoustic wave detection element according to claim 1, wherein the resin is polytetrafluoroethylene.   The sound wave detecting element according to any one of claims 1 to 3, wherein the porous resin body includes a nonwoven fabric or a woven fabric formed from fibers made of a resin.   The sound wave detecting element according to claim 4 whose average fiber diameter of said fiber is 0.05-50 micrometers.   The sound wave detecting element according to claim 1, wherein the porous resin body is subjected to polarization treatment.   The sound wave detecting element according to any one of claims 1 to 6, wherein a sound wave transmittance of the pressure vessel is 20% or more.   The sound wave detecting element according to claim 1, wherein the pressure vessel has a tensile strength of 50 to 2000 MPa.   The sound wave detecting element according to claim 1, wherein the porous resin body is accommodated in the pressure vessel.