WO2010001633A1 - Organic piezoelectric material, process for producing the organic piezoelectric material, ultrasonic vibrator, and ultrasonic image diagnosis apparatus for medical application - Google Patents

Organic piezoelectric material, process for producing the organic piezoelectric material, ultrasonic vibrator, and ultrasonic image diagnosis apparatus for medical application Download PDF

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Publication number
WO2010001633A1
WO2010001633A1 PCT/JP2009/053372 JP2009053372W WO2010001633A1 WO 2010001633 A1 WO2010001633 A1 WO 2010001633A1 JP 2009053372 W JP2009053372 W JP 2009053372W WO 2010001633 A1 WO2010001633 A1 WO 2010001633A1
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piezoelectric material
organic piezoelectric
ultrasonic
organic
piezoelectric
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PCT/JP2009/053372
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French (fr)
Japanese (ja)
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大沼　憲司
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コニカミノルタエムジー株式会社
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
    • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
    • B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
    • B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
    • B06B1/06—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/01—Manufacture or treatment
    • H10N30/09—Forming piezoelectric or electrostrictive materials
    • H10N30/098—Forming organic materials
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/80—Constructional details
    • H10N30/85—Piezoelectric or electrostrictive active materials
    • H10N30/857—Macromolecular compositions

Definitions

  • the present invention relates to an organic piezoelectric material for constructing an ultrasonic transducer suitable for a high frequency and a wide band, a manufacturing method thereof, an ultrasonic transducer, and an ultrasonic medical image diagnostic apparatus using the organic piezoelectric material.
  • Ultrasound is a general term for sound waves of 16 kHz or higher, and can be examined non-destructively and harmlessly, so it is applied to various fields such as defect inspection and disease diagnosis.
  • an ultrasonic diagnosis that scans the inside of a subject with ultrasound and images the internal state of the subject based on a reception signal generated from a reflected wave (echo) of the ultrasound from the inside of the subject.
  • a device In this ultrasonic diagnostic apparatus, an ultrasonic probe that transmits and receives ultrasonic waves to and from a subject is used.
  • a transducer that generates a received signal by receiving a reflected wave of an ultrasonic wave generated by a difference in acoustic impedance inside a subject is generated by mechanical vibration based on a transmission signal.
  • An ultrasonic transmitting / receiving element configured to be provided is used.
  • harmonic imaging that forms an image of the internal state in the subject using the harmonic frequency component, not the frequency (fundamental frequency) component of the ultrasound transmitted from the ultrasound probe into the subject
  • Harmonic Imaging technology has (1) a low sidelobe level compared to the level of the fundamental frequency component, an improved S / N ratio (signal to noise ratio) and improved contrast resolution, and (2) frequency Increasing the beam width narrows and the lateral resolution is improved. (3) Since the sound pressure is small and the fluctuation of the sound pressure is small at a short distance, multiple reflections are suppressed. (4) Focus It has various advantages such as a greater depth speed compared to the case where the further attenuation is the same as the fundamental wave and the high frequency is the fundamental wave.
  • This ultrasonic probe for harmonic imaging requires a wide frequency band from the frequency of the fundamental wave to the frequency of the harmonic, and its lower frequency range is used for transmission to transmit the fundamental wave. Is done.
  • the frequency region on the high frequency side is used for reception for receiving harmonics (see, for example, Patent Document 1).
  • the ultrasonic probe disclosed in Patent Document 1 receives an ultrasonic wave that is applied to a subject, transmits an ultrasonic wave into the subject, and is reflected and returned within the subject. It is an acoustic probe.
  • the ultrasonic probe transmits a fundamental wave composed of ultrasonic waves having a predetermined center frequency, which is composed of a plurality of arranged first piezoelectric elements having a predetermined first acoustic impedance, into the subject. , And a first piezoelectric layer responsible for receiving the fundamental wave of the ultrasonic waves reflected back within the subject.
  • a higher harmonic wave of ultrasonic waves reflected and returned from the subject which includes a plurality of second piezoelectric elements arranged with a predetermined second acoustic impedance smaller than the first acoustic impedance.
  • a second piezoelectric layer responsible for receiving waves is provided.
  • the second piezoelectric layer is overlaid on the entire surface of the first piezoelectric layer on the side where the ultrasonic probe is applied to the subject. Therefore, the ultrasonic probe can transmit and receive ultrasonic waves in a wide frequency band with such a configuration.
  • the fundamental wave in harmonic imaging is preferably a sound wave having the narrowest possible bandwidth.
  • the piezoelectric element responsible for this is a so-called polarization treatment of a single crystal such as quartz, LiNbO 3 , LiTaO 3 , KNbO 3 , a thin film such as ZnO or AlN, or a sintered body such as Pb (Zr, Ti) O 3. Ceramic inorganic piezoelectric materials are widely used. Piezoelectric elements that detect received waves on the high frequency side require a wider bandwidth sensitivity, and these inorganic materials are not suitable.
  • an organic piezoelectric body using an organic polymer material such as polyvinylidene fluoride (hereinafter also abbreviated as “PVDF”) is known (see, for example, Patent Document 2).
  • PVDF polyvinylidene fluoride
  • this organic piezoelectric material has greater flexibility, and can be made into any shape and form, making it easier to reduce the thickness, area, and length. Have.
  • the organic piezoelectric element is different from the inorganic piezoelectric element in its manufacturing method
  • the polymerization reaction unreacted substance contained in the sample in the manufacturing process that is, the low molecular weight monomer is the piezoelectric characteristic of the piezoelectric body. May affect storage. Specifically, when an organic material is produced by a polymerization reaction, if the reaction is not sufficient, that is, if the amount of residual monomer is large, the amount of polarization is reduced by diffusion and flow of the remaining monomer molecules during storage even if polarization treatment is performed. It may change. In the conventional method, it is known that a low molecular weight component remaining after polymerization is degassed by an autoclave or the like (see, for example, Patent Document 3).
  • the present invention has been made in view of the above-described problems and situations, and a solution to the problem is an organic piezoelectric material for forming an ultrasonic transducer that is excellent in piezoelectric characteristics and suitable for a high frequency and a wide band, and a manufacturing method thereof.
  • An ultrasonic probe using the same, and an ultrasonic medical diagnostic imaging apparatus are provided.
  • An organic piezoelectric material comprising a high molecular weight material for forming an ultrasonic vibrator, wherein the amount of residual monomer contained in the organic piezoelectric material is 200 ppm or less.
  • the electromechanical coupling constant of the organic piezoelectric material immediately after the polarization treatment is 0.3 to 0.4, and the electromechanical coupling constant after storing the organic piezoelectric material immediately after the polarization treatment at 50 ° C. in an environment for 300 hours is 4.
  • the organic piezoelectric material is made of a copolymer of vinylidene fluoride and trifluoroethylene, and the ratio of vinylidene fluoride is 95 to 60 mol% and trifluoroethylene is 5 to 40 mol%. 5.
  • the organic piezoelectric material according to any one of 1 to 4.
  • Ultrasound in which a means for generating an electrical signal and a plurality of transducers for receiving the electrical signal and transmitting an ultrasonic wave toward the subject and generating a reception signal corresponding to the reflected wave received from the subject are arranged
  • the ultrasonic medical image diagnostic apparatus comprising: an ultrasonic probe; and an image processing unit that generates an image of the subject according to the reception signal generated by the ultrasonic probe.
  • Comprising both a transmitting ultrasonic transducer and a receiving ultrasonic transducer, and one or both of the ultrasonic transducers is the ultrasonic transducer according to 7 above, Ultrasonic medical diagnostic imaging device.
  • an organic piezoelectric material that is excellent in piezoelectric characteristics and heat resistance and that is suitable for high frequency and wide band, an organic piezoelectric material for manufacturing the same, an ultrasonic probe using the same, and An ultrasonic medical image diagnostic apparatus can be provided.
  • the ultrasonic transducer of the present invention is an ultrasonic transducer having an ultrasonic piezoelectric material used for a probe for an ultrasonic medical diagnostic imaging apparatus, and the ultrasonic piezoelectric material is mainly composed of vinylidene fluoride. It is an organic piezoelectric material, and the amount of residual monomer contained per unit mass of the organic piezoelectric material is 200 ppm or less, and this feature is a technical feature common to the inventions according to claims 1 to 5.
  • the organic piezoelectric material is stretched and formed from the viewpoint of piezoelectric characteristics.
  • a method for manufacturing the ultrasonic vibrator of the present invention a method for manufacturing an aspect in which polarization treatment is performed either before forming electrodes to be installed on both sides of an organic piezoelectric film, after forming electrodes on only one side, or after forming electrodes on both sides. It is preferable that Moreover, it is preferable that the said polarization process is a voltage application process.
  • the ultrasonic transducer of the present invention can be combined with other ultrasonic transducers to constitute an ultrasonic probe.
  • the ultrasonic probe may be an organic piezoelectric material of the same type as the ultrasonic transducer of the present invention, or another known piezoelectric material, and the piezoelectric material may be an inorganic material or a polymer material, and further combined.
  • the material may be another polymeric material that is not a piezoelectric material.
  • the ultrasonic probe is preferably a laminated vibrator having two or more layers formed by bonding the above materials, and the laminated vibrator has a thickness of 20 to 600 ⁇ m.
  • the ultrasonic transducer of the present invention or an ultrasonic probe using the ultrasonic transducer can be suitably used for an ultrasonic medical image diagnostic apparatus.
  • the ultrasonic transducer is used for a probe for an ultrasonic medical diagnostic imaging apparatus including an ultrasonic transmission transducer and an ultrasonic reception transducer.
  • an ultrasonic transducer is configured by arranging a pair of electrodes with a layer (or film) (hereinafter referred to as a piezoelectric layer) or a “piezoelectric film” made of a film-like piezoelectric material in between.
  • a piezoelectric layer a layer (or film)
  • piezoelectric film a layer made of a film-like piezoelectric material in between.
  • an ultrasonic probe is configured by one-dimensionally arranging the transducers.
  • a predetermined number of transducers in the major axis direction in which a plurality of transducers are arranged is set as the aperture, and the plurality of transducers belonging to the aperture are driven to converge the ultrasonic beam on the measurement site in the subject. And has a function of receiving reflected echoes of ultrasonic waves emitted from the subject by a plurality of transducers belonging to the aperture and converting them into electrical signals.
  • Organic piezoelectric material as the constituent material of the piezoelectric material constituting the ultrasonic vibrator of the present invention can be adopted regardless of whether it is a low molecular material or a high molecular material.
  • a high molecular organic piezoelectric material for example, polyvinylidene fluoride, a polyvinylidene fluoride copolymer, a polyvinylidene cyanide or a vinylidene cyanide copolymer, an odd-numbered nylon such as nylon 9 or nylon 11, or an aromatic Aromatic nylon, alicyclic nylon, polylactic acid, polyhydroxycarboxylic acids such as polyhydroxybutyrate, cellulose derivatives, polyurea and the like. From the viewpoint of good piezoelectric properties, processability, availability, etc., it is necessary to be a polymer organic piezoelectric material, particularly a polymer material mainly composed of vinylidene fluoride.
  • the electromechanical coupling constant (piezoelectric effect) in the thickness direction varies depending on the copolymerization ratio, so that the former copolymerization ratio is 60 to 99 mol%. Further, it is preferably 85 to 99 mol%.
  • a polymer containing 85 to 99 mol% of vinylidene fluoride and 1 to 15 mol% of perfluoroalkyl vinyl ether, perfluoroalkoxyethylene, perfluorohexaethylene, etc. is composed of an inorganic piezoelectric element for transmission and an organic piezoelectric element for reception. In combination with the element, it is possible to suppress the transmission fundamental wave and increase the sensitivity of harmonic reception.
  • the organic piezoelectric material can be made thinner than an inorganic piezoelectric material made of ceramics, the organic piezoelectric material is characterized in that it can be used as a vibrator corresponding to transmission and reception of higher frequencies.
  • the organic piezoelectric material has a relative dielectric constant of 10 to 50 at a thickness resonance frequency. Adjustment of the relative dielectric constant is performed by CF 2 contained in a compound constituting the organic piezoelectric material. It can be carried out by adjusting the quantity, composition, degree of polymerization, etc. of polar functional groups such as groups and CN groups, and polarization treatment described later.
  • the organic piezoelectric film constituting the vibrator of the present invention may be configured by laminating a plurality of polymer materials.
  • the polymer material to be laminated the following polymer material having a relatively low relative dielectric constant can be used in addition to the above polymer material.
  • the numerical value in parentheses indicates the relative dielectric constant of the polymer material (resin).
  • the polymer material having a low relative dielectric constant is preferably selected in accordance with various purposes such as adjusting the piezoelectric characteristics or imparting the physical strength of the organic piezoelectric film. .
  • the residual monomer contained in the organic piezoelectric material in the present invention is a small amount of low molecular weight monomer that has not been converted when the polymer material is produced by the polymerization process.
  • a radical generating species such as an initiator is newly added to the system immediately before the end of polymerization, and a product and unreacted substances are separated using a washing process after the end of polymerization. Separation under reduced pressure, and the like.
  • the organic piezoelectric material of the present invention if the amount of residual monomer is large, dielectric breakdown is very likely to occur through the low-molecular monomer during the polarization treatment, and the piezoelectric performance is reduced because the molecular motion during storage is promoted. End up.
  • the organic piezoelectric film according to the present invention can be produced by various methods using the polymer material as a main constituent.
  • a method for producing an organic piezoelectric film basically, a solution obtained by applying a solution of the polymer material on a substrate and drying it, or a conventionally known vapor deposition weight using a raw material compound of the polymer material is used.
  • a method of forming a polymer film by a combination method, a solution polymerization coating method, or the like can be employed.
  • JP-A-7-258370, JP-A-5-311399, and JP-A-2006-49418 can be referred to.
  • the specific method and conditions of the solution polymerization coating method can be performed according to various conventionally known methods. For example, a mixed solution of raw materials is applied onto a substrate, dried to some extent under reduced pressure conditions (after the solvent is removed), heated, thermally polymerized, and then or simultaneously polarized to form an organic piezoelectric film. The method is preferred.
  • the organic piezoelectric material containing vinylidene fluoride according to the present invention is used as a vibrator, it is generally formed in a film shape and then a surface electrode for inputting an electric signal.
  • a general method such as a melting method or a casting method can be used.
  • a polyvinylidene fluoride-trifluoroethylene copolymer it is known that it has a crystalline form with spontaneous polarization only when it is made into a film, but in order to further improve the characteristics, a process for aligning the molecular arrangement should be added. Is useful. Examples of means include stretching film formation and polarization treatment.
  • the stretching film forming method various known methods can be employed. For example, a solution obtained by dissolving the above polymer material in an organic solvent such as ethyl methyl ketone (MEK) is cast on a substrate such as a glass plate, and the solvent is dried at room temperature to obtain a film having a desired thickness. The film is stretched to a predetermined length at room temperature. The stretching can be performed in a uniaxial / biaxial direction so that the organic piezoelectric film having a predetermined shape is not broken.
  • the draw ratio is 2 to 10 times, preferably 2 to 6 times.
  • the melt flow rate at 230 ° C. is 0.03 g / min or less. More preferably, a high-sensitivity piezoelectric thin film can be obtained by using a polymer piezoelectric material of 0.02 g / min or less, more preferably 0.01 g / min or less.
  • Polarization treatment As a polarization treatment method in the polarization treatment according to the present invention, a conventionally known method such as DC voltage application treatment, AC voltage application treatment, or corona discharge treatment can be applied.
  • the corona discharge treatment can be performed by using a commercially available apparatus comprising a high voltage power source and electrodes.
  • the voltage of the high voltage power source is preferably ⁇ 1 to ⁇ 20 kV, the current is 1 to 80 mA, the distance between the electrodes is preferably 1 to 10 cm, and the applied voltage is preferably 0.5 to 2.0 MV / m. .
  • electrodes needle-like electrodes, linear electrodes (wire electrodes), and mesh electrodes conventionally used are preferable, but the invention is not limited thereto.
  • the selection of the substrate differs depending on the application and use method of the organic piezoelectric film according to the present invention.
  • a plastic plate or film such as polyimide, polyamide, polyimide amide, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polymethyl methacrylate (PMMA), polycarbonate resin, or cycloolefin polymer is used.
  • PET polyethylene terephthalate
  • PEN polyethylene naphthalate
  • PMMA polymethyl methacrylate
  • the surface of these materials may be covered with aluminum, gold, copper, magnesium, silicon or the like.
  • a single crystal plate or film of aluminum, gold, copper, magnesium, silicon alone, or a rare earth halide may be used.
  • the vibrator having the piezoelectric material according to the present invention is manufactured by forming electrodes on both surfaces or one surface of a piezoelectric film (layer) and polarizing the piezoelectric film.
  • the electrode is formed using an electrode material mainly composed of gold (Au), platinum (Pt), silver (Ag), palladium (Pd), copper (Cu), nickel (Ni), tin (Sn), or the like. .
  • a base metal such as titanium (Ti) or chromium (Cr) is formed to a thickness of 0.02 to 1.0 ⁇ m by sputtering.
  • these electrodes can be formed by screen printing, dipping, or thermal spraying using a conductive paste in which fine metal powder and low-melting glass are mixed.
  • a piezoelectric element can be obtained by supplying a predetermined voltage between the electrodes formed on both surfaces of the piezoelectric film to polarize the piezoelectric film.
  • An ultrasonic probe according to the present invention is a probe for an ultrasonic medical diagnostic imaging apparatus including an ultrasonic transmission transducer and an ultrasonic reception transducer, and the ultrasonic reception according to the present invention.
  • a vibrator is used.
  • both the transmission and reception of ultrasonic waves may be performed by a single transducer, but more preferably, the transducer is configured separately for transmission and reception in the probe.
  • the piezoelectric material constituting the transmitting vibrator may be a conventionally known ceramic inorganic piezoelectric material or an organic piezoelectric material.
  • the ultrasonic receiving transducer of the present invention can be arranged on or in parallel with the transmitting transducer.
  • the structure for laminating the ultrasonic receiving transducer of the present invention on the ultrasonic transmitting transducer is good, and in this case, the ultrasonic receiving transducer of the present invention is another high-frequency transducer.
  • the film thickness of the receiving vibrator and the other polymer material be matched to a preferable receiving frequency band in terms of probe design. In view of a practical ultrasonic medical image diagnostic apparatus and biological information collection from a practical frequency band, the film thickness is preferably 40 to 150 ⁇ m.
  • the probe may be provided with a backing layer, an acoustic matching layer, an acoustic lens, and the like. Also, a probe in which vibrators having a large number of piezoelectric materials are two-dimensionally arranged can be used. A plurality of two-dimensionally arranged probes can be sequentially scanned to form a scanner.
  • the ultrasonic probe according to the present invention can be used for various types of ultrasonic diagnostic apparatuses.
  • an ultrasonic probe probe
  • piezoelectric body transducers that transmit ultrasonic waves to a subject such as a patient and receive ultrasonic waves reflected from the subject as echo signals is arranged
  • An ultrasonic medical diagnostic imaging apparatus is preferred.
  • an electric signal is supplied to the ultrasonic probe to generate an ultrasonic wave, and a transmission / reception circuit that receives an echo signal received by each piezoelectric vibrator of the ultrasonic probe, and transmission / reception control of the transmission / reception circuit It is preferable that a transmission / reception control circuit for performing the above is provided.
  • the display control unit includes an image data conversion circuit that converts the echo signal received by the transmission / reception circuit into ultrasonic image data of the subject, and controls and displays the monitor with the ultrasonic image data converted by the image data conversion circuit.
  • An ultrasonic medical image diagnostic apparatus including a circuit and a control circuit that controls the entire ultrasonic medical image diagnostic apparatus is preferable.
  • a transmission / reception control circuit, an image data conversion circuit, and a display control circuit are connected to a control circuit, and the control circuit controls operations of these units. Then, an electrical signal is applied to each piezoelectric vibrator of the ultrasonic probe to transmit an ultrasonic wave to the subject, and the reflected wave caused by acoustic impedance mismatch inside the subject is detected by the ultrasonic probe. Receive at.
  • the transmission / reception circuit corresponds to “means for generating an electric signal”
  • the image data conversion circuit corresponds to “image processing means”.
  • the ultrasonic diagnostic apparatus by utilizing the characteristics of the ultrasonic wave receiving vibrator excellent in piezoelectric characteristics and heat resistance of the present invention and suitable for high frequency and wide band, the image quality and its An ultrasonic image with improved reproduction and stability can be obtained.
  • Example 1 Polyvinylidene fluoride copolymer powder (weight average molecular weight 290,000) having a molar ratio of vinylidene fluoride (hereinafter VDF) and trifluoroethylene (hereinafter 3FE) of 75:25 is dried at 50 ° C. for 12 hours in a vacuum oven. It was. Next, a solution of this powder in a 9: 1 mixed solvent of ethyl methyl ketone (hereinafter referred to as MEK) and dimethylformamide (hereinafter referred to as DMF) heated to 50 ° C. was cast on a glass plate. Thereafter, the solvent was dried at 50 ° C.
  • MEK ethyl methyl ketone
  • DMF dimethylformamide
  • a film organic piezoelectric film having a thickness of about 140 ⁇ m.
  • This film was stretched 4 times at room temperature, and then heat treated at 135 ° C. for 1 hour while maintaining the stretched length.
  • the film thickness after heat treatment was 43 ⁇ m.
  • a sample with a surface electrode was obtained by vapor-depositing gold / aluminum on both surfaces of the film obtained here so that the surface resistance was 20 ⁇ or less.
  • the electrode was subjected to polarization treatment while applying an AC voltage of 0.1 Hz at room temperature.
  • the polarization treatment was performed from a low voltage, and the voltage was gradually applied until the electric field between the electrodes finally reached 100 MV / m.
  • the final polarization amount was obtained from the residual polarization amount when the piezoelectric material was regarded as a capacitor, that is, the film thickness, the electrode area, and the charge accumulation amount with respect to the applied electric field, and Sample 1 of the present invention was obtained.
  • Electrode durability [Method for evaluating organic piezoelectric film]
  • Lead wires are attached to the electrodes on both sides of the sample with the electrode obtained as described above, and frequency scanning is performed at 600 points at equal intervals from 40 Hz to 110 MHz in an atmosphere of 25 ° C. using an impedance analyzer 4294A manufactured by Agilent Technologies. did. The value of the relative dielectric constant at the thickness resonance frequency was obtained. Similarly, when the peak frequency P of the resistance value near the thickness resonance frequency and the peak frequency S of the conductance were obtained, the electromechanical coupling constant kt was obtained by the following equation .
  • FIG. 1 shows hysteresis curves of remanent polarization amounts of the sample 1 of the present invention and the sample 3 for comparison.
  • FIG. 2 shows a time course graph of the electromechanical coupling constant.
  • Example 2 (Preparation and evaluation of ultrasonic probe) (Production of piezoelectric material for transmission) Component raw materials CaCO 3 , La 2 O 3 , Bi 2 O 3 and TiO 2 , and subcomponent raw materials MnO are prepared, and for the component raw materials, the final composition of the components is (Ca 0. 97 La 0.0 3 . ) Bi 4 . Weighed to be 01 Ti 4 O 15 . Next, pure water was added, mixed in a ball mill containing zirconia media in pure water for 8 hours, and sufficiently dried to obtain a mixed powder. The obtained mixed powder was temporarily molded and calcined in air at 800 ° C. for 2 hours to prepare a calcined product.
  • the piezoelectric ceramic raw material powder having a particle diameter of 100 nm was obtained by changing the pulverization time and pulverization conditions. 6% by mass of pure water as a binder is added to each piezoelectric ceramic raw material powder having a different particle diameter, press-molded to form a plate-shaped temporary molded body having a thickness of 100 ⁇ m, and this plate-shaped temporary molded body is vacuum-packed and then 235 MPa. It shape
  • an ultrasonic probe was prototyped by laminating a laminated receiving transducer on the above-described piezoelectric material for transmission, and installing a backing layer and an acoustic matching layer.
  • a laminated resonator for reception using only a polyvinylidene fluoride copolymer film (organic piezoelectric film) was laminated on the above laminated resonator.
  • a probe similar to the above-described ultrasonic probe was produced.
  • the reception sensitivity is originating the fundamental frequency f 1 of 5 MHz, to determine the received relative sensitivity of 20MHz as 15 MHz, 4 harmonics as received second harmonic wave f 2 as 10 MHz, 3 harmonic.
  • a sound intensity measurement system Model 805 (1 to 50 MHz) of Sonora Medical System, Inc. (Sonora Medical System, Inc: 2021 Miller Drive Longmont, Colorado (0501 USA)) was used.
  • the dielectric breakdown strength was measured by multiplying the load power P by 5 times, testing for 10 hours, and then returning the load power to the standard to evaluate the relative reception sensitivity.
  • the sensitivity was evaluated as good when the decrease in sensitivity was within 1% before the load test, more than 1% and less than 10%, and 10% or more as bad.
  • the probe including the receiving piezoelectric (body) laminated vibrator according to the present invention has a relative receiving sensitivity about 1.2 times that of the comparative example, and the dielectric breakdown strength is It was confirmed to be good. That is, it was confirmed that the ultrasonic transducer of the present invention can be suitably used for an ultrasonic probe used in an ultrasonic medical image diagnostic apparatus.

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Abstract

This invention provides an organic piezoelectric material for constituting an ultrasonic vibrator, which has excellent piezoelectric properties and is suitable in high-frequency and broad bands, a process for producing the organic piezoelectric material, an ultrasonic probe using the organic piezoelectric material, and an ultrasonic image diagnosis apparatus for medical application. The organic piezoelectric material is an organic piezoelectric material formed of a high-molecular weight material for ultrasonic vibrator formation. The organic piezoelectric material is characterized in that the content of the residual monomer in the organic piezoelectric material is not more than 200 ppm.

Description

有機圧電材料とその製造方法、超音波振動子、超音波医用画像診断装置Organic piezoelectric material and manufacturing method thereof, ultrasonic transducer, ultrasonic medical diagnostic imaging apparatus
　本発明は、高周波・広帯域に適した超音波振動子を構成するための有機圧電材料、その製造方法、超音波振動子、及び、それを用いた超音波医用画像診断装置に関する。 The present invention relates to an organic piezoelectric material for constructing an ultrasonic transducer suitable for a high frequency and a wide band, a manufacturing method thereof, an ultrasonic transducer, and an ultrasonic medical image diagnostic apparatus using the organic piezoelectric material.
　超音波とは、通常、１６ｋＨｚ以上の音波を総称して言い、非破壊および無害でその内部を調べることが可能なことから、欠陥の検査や疾患の診断などの様々な分野に応用されている。その一つに、被検体内を超音波で走査し、被検体内からの超音波の反射波（エコー）から生成した受信信号に基づいて当該被検体内の内部状態を画像化する超音波診断装置がある。この超音波診断装置では、被検体に対して超音波を送受信する超音波探触子が用いられている。この超音波探触子としては、送信信号に基づいて機械振動して超音波を発生し、被検体内部で音響インピーダンスの違いによって生じる超音波の反射波を受けて受信信号を生成する振動子を備えて構成される超音波送受信素子が用いられる。 Ultrasound is a general term for sound waves of 16 kHz or higher, and can be examined non-destructively and harmlessly, so it is applied to various fields such as defect inspection and disease diagnosis. . For example, an ultrasonic diagnosis that scans the inside of a subject with ultrasound and images the internal state of the subject based on a reception signal generated from a reflected wave (echo) of the ultrasound from the inside of the subject. There is a device. In this ultrasonic diagnostic apparatus, an ultrasonic probe that transmits and receives ultrasonic waves to and from a subject is used. As this ultrasonic probe, a transducer that generates a received signal by receiving a reflected wave of an ultrasonic wave generated by a difference in acoustic impedance inside a subject is generated by mechanical vibration based on a transmission signal. An ultrasonic transmitting / receiving element configured to be provided is used.
　そして、近年では、超音波探触子から被検体内へ送信された超音波の周波数（基本周波数）成分ではなく、その高調波周波数成分によって被検体内の内部状態の画像を形成するハーモニックイメージング（Ｈａｒｍｏｎｉｃ　Ｉｍａｇｉｎｇ）技術が研究、開発されている。このハーモニックイメージング技術は、（１）基本周波数成分のレベルに比較してサイドローブレベルが小さく、Ｓ／Ｎ比（ｓｉｇｎａｌ　ｔｏ　ｎｏｉｓｅ　ｒａｔｉｏ）が良くなってコントラスト分解能が向上すること、（２）周波数が高くなることによってビーム幅が細くなって横方向分解能が向上すること、（３）近距離では音圧が小さくて音圧の変動が少ないために多重反射が抑制されること、および（４）焦点以遠の減衰が基本波並みであり高周波を基本波とする場合に較べて深速度を大きく取れることなどの様々な利点を有している。 In recent years, harmonic imaging that forms an image of the internal state in the subject using the harmonic frequency component, not the frequency (fundamental frequency) component of the ultrasound transmitted from the ultrasound probe into the subject ( Harmonic Imaging technology is being researched and developed. This harmonic imaging technology has (1) a low sidelobe level compared to the level of the fundamental frequency component, an improved S / N ratio (signal to noise ratio) and improved contrast resolution, and (2) frequency Increasing the beam width narrows and the lateral resolution is improved. (3) Since the sound pressure is small and the fluctuation of the sound pressure is small at a short distance, multiple reflections are suppressed. (4) Focus It has various advantages such as a greater depth speed compared to the case where the further attenuation is the same as the fundamental wave and the high frequency is the fundamental wave.
　このハーモニックイメージング用の超音波探触子は、基本波の周波数から高調波の周波数までの広い周波数帯域が必要とされ、その低周波側の周波数領域が基本波を送信するための送信用に利用される。一方、その高周波側の周波数領域が高調波を受信するための受信用に利用される（例えば特許文献１参照）。 This ultrasonic probe for harmonic imaging requires a wide frequency band from the frequency of the fundamental wave to the frequency of the harmonic, and its lower frequency range is used for transmission to transmit the fundamental wave. Is done. On the other hand, the frequency region on the high frequency side is used for reception for receiving harmonics (see, for example, Patent Document 1).
　この特許文献１に開示されている超音波探触子は、被検体にあてがわれて当該被検体内に超音波を送信し当該被検体内で反射して戻ってきた超音波を受信する超音波探触子である。この超音波探触子は、所定の第１の音響インピーダンスを有する配列された複数の第１の圧電素子からなる、所定の中心周波数の超音波からなる基本波の、被検体内に向けた送信、および当該被検体内で反射して戻ってきた超音波のうちの基本波の受信を担う第１圧電層を備えている。また、前記第１の音響インピーダンスよりも小さい所定の第２の音響インピーダンスを有する配列された複数の第２の圧電素子からなる、前記被検体内で反射して戻ってきた超音波のうちの高調波の受信を担う第２圧電層を備えている。なお、当該第２圧電層は、前記第１圧電層の、この超音波探触子が被検体にあてがわれる側の全面に重ねられている。したがって、当該超音波探触子は、このような構成によって広い周波数帯域で超音波を送受信することができる。 The ultrasonic probe disclosed in Patent Document 1 receives an ultrasonic wave that is applied to a subject, transmits an ultrasonic wave into the subject, and is reflected and returned within the subject. It is an acoustic probe. The ultrasonic probe transmits a fundamental wave composed of ultrasonic waves having a predetermined center frequency, which is composed of a plurality of arranged first piezoelectric elements having a predetermined first acoustic impedance, into the subject. , And a first piezoelectric layer responsible for receiving the fundamental wave of the ultrasonic waves reflected back within the subject. Further, a higher harmonic wave of ultrasonic waves reflected and returned from the subject, which includes a plurality of second piezoelectric elements arranged with a predetermined second acoustic impedance smaller than the first acoustic impedance. A second piezoelectric layer responsible for receiving waves is provided. The second piezoelectric layer is overlaid on the entire surface of the first piezoelectric layer on the side where the ultrasonic probe is applied to the subject. Therefore, the ultrasonic probe can transmit and receive ultrasonic waves in a wide frequency band with such a configuration.
　ハーモニックイメージングにおける基本波は、出来る限り狭い帯域巾を有する音波がよい。それを担う圧電素子には、水晶、ＬｉＮｂＯ３、ＬｉＴａＯ３、ＫＮｂＯ３などの単結晶、ＺｎＯ、ＡｌＮなどの薄膜、Ｐｂ（Ｚｒ，Ｔｉ）Ｏ３系などの焼結体を分極処理した、いわゆるセラミックスの無機圧電体が広く利用されている。高周波側の受信波を検知する圧電素子には、より広い帯域巾の感度が必要でこれらの無機材料は適さない。高周波、広帯域に適した圧電素子として、ポリフッ化ビニリデン（以下「ＰＶＤＦ」とも略称する。）などの有機系高分子物質を利用した有機圧電体が知られている（例えば特許文献２参照）。この有機圧電体は、無機圧電体と比較して、可撓性が大きく、薄膜化、大面積化、長尺化が容易で任意の形状、形態のものを作ることができる、等の特性を有する。 The fundamental wave in harmonic imaging is preferably a sound wave having the narrowest possible bandwidth. The piezoelectric element responsible for this is a so-called polarization treatment of a single crystal such as quartz, LiNbO 3 , LiTaO 3 , KNbO 3 , a thin film such as ZnO or AlN, or a sintered body such as Pb (Zr, Ti) O 3. Ceramic inorganic piezoelectric materials are widely used. Piezoelectric elements that detect received waves on the high frequency side require a wider bandwidth sensitivity, and these inorganic materials are not suitable. As a piezoelectric element suitable for a high frequency and a wide band, an organic piezoelectric body using an organic polymer material such as polyvinylidene fluoride (hereinafter also abbreviated as “PVDF”) is known (see, for example, Patent Document 2). Compared to inorganic piezoelectric materials, this organic piezoelectric material has greater flexibility, and can be made into any shape and form, making it easier to reduce the thickness, area, and length. Have.
　しかしながら、この有機圧電体からなる素子は、無機圧電体からなる素子と異なる製造方法ゆえに、試料中に製造工程中で含まれる重合反応未反応物、すなわち低分子量のモノマーが圧電体の圧電特性の保存性に影響を及ぼすことがある。具体的には、有機材料を重合反応によって作製する際に、反応が十分でない、すなわち残留モノマー量が多いと、分極処理をしても残モノマー分子が保存時に拡散・流動することで分極量が変わってしまうことがある。従来方法では重合後に残留する低分子量成分をオートクレーブ等で脱気することが知られている（例えば特許文献３参照）。これらの有機圧電体が超音波診断装置用の振動子に使用するために表面に金属電極薄膜を塗設するが、圧電体中に残留モノマーが多く含まれていると、接着耐久性が十分でないことが分かった。
特開平１１－２７６４７８号公報 特開昭６０－２１７６７４号公報 特開平２－１７０９号公報 However, because the organic piezoelectric element is different from the inorganic piezoelectric element in its manufacturing method, the polymerization reaction unreacted substance contained in the sample in the manufacturing process, that is, the low molecular weight monomer is the piezoelectric characteristic of the piezoelectric body. May affect storage. Specifically, when an organic material is produced by a polymerization reaction, if the reaction is not sufficient, that is, if the amount of residual monomer is large, the amount of polarization is reduced by diffusion and flow of the remaining monomer molecules during storage even if polarization treatment is performed. It may change. In the conventional method, it is known that a low molecular weight component remaining after polymerization is degassed by an autoclave or the like (see, for example, Patent Document 3). These organic piezoelectric bodies are coated with a metal electrode thin film on the surface so that they can be used in a vibrator for an ultrasonic diagnostic apparatus. However, if a large amount of residual monomer is contained in the piezoelectric body, the adhesion durability is not sufficient. I understood that.
Japanese Patent Laid-Open No. 11-276478 JP-A-60-217674 Japanese Patent Laid-Open No. 2-1709
　本発明は、上記問題・状況に鑑みてなされたものであり、その解決課題は、圧電特性に優れ、かつ高周波・広帯域に適した超音波振動子を構成するための有機圧電材料、その製造方法、それを用いた超音波探触子、及び超音波医用画像診断装置を提供することである。 The present invention has been made in view of the above-described problems and situations, and a solution to the problem is an organic piezoelectric material for forming an ultrasonic transducer that is excellent in piezoelectric characteristics and suitable for a high frequency and a wide band, and a manufacturing method thereof. An ultrasonic probe using the same, and an ultrasonic medical diagnostic imaging apparatus are provided.
　本発明の上記目的は、以下の構成により達成することができる。 The above object of the present invention can be achieved by the following configuration.
　１．超音波振動子を形成するための高分子量体からなる有機圧電材料であって、該有機圧電材料に含まれる、残モノマー量が２００ｐｐｍ以下であることを特徴とする有機圧電材料。 1. An organic piezoelectric material comprising a high molecular weight material for forming an ultrasonic vibrator, wherein the amount of residual monomer contained in the organic piezoelectric material is 200 ppm or less.
　２．分極処理を経て形成される有機圧電材料であって、分極処理を施される前の前記有機圧電材料に含まれる、残モノマー量が２００ｐｐｍ以下であることを特徴とする前記１に記載の有機圧電材料。 2. 2. The organic piezoelectric material according to the item 1, wherein the organic piezoelectric material is formed through a polarization treatment, and a residual monomer amount contained in the organic piezoelectric material before the polarization treatment is 200 ppm or less. material.
　３．有機圧電材料が延伸製膜工程を経て形成されていることを特徴とする前記１又は２に記載の有機圧電材料。 3. 3. The organic piezoelectric material as described in 1 or 2 above, wherein the organic piezoelectric material is formed through a stretching film forming step.
　４．分極処理直後の有機圧電材料の電気機械結合定数が０．３～０．４であって、かつ前記分極処理直後の有機圧電材料を５０℃で環境下３００時間保存した後の電気機械結合定数が０．３～０．４であることを特徴とする前記３に記載の有機圧電材料。 4. The electromechanical coupling constant of the organic piezoelectric material immediately after the polarization treatment is 0.3 to 0.4, and the electromechanical coupling constant after storing the organic piezoelectric material immediately after the polarization treatment at 50 ° C. in an environment for 300 hours is 4. The organic piezoelectric material as described in 3 above, wherein the organic piezoelectric material is 0.3 to 0.4.
　５．前記有機圧電材料が、フッ化ビニリデンとトリフルオロエチレンの共重合体からなり、フッ化ビニリデンが９５～６０モル％、トリフルオロエチレン５～４０モル％の比率の範囲であることを特徴とする前記１～４のいずれか１項に記載の有機圧電材料。 5. The organic piezoelectric material is made of a copolymer of vinylidene fluoride and trifluoroethylene, and the ratio of vinylidene fluoride is 95 to 60 mol% and trifluoroethylene is 5 to 40 mol%. 5. The organic piezoelectric material according to any one of 1 to 4.
　６．前記１～５のいずれか１項に記載の有機圧電材料の製造方法であって、該有機圧電材料の原料となる高分子量体を有機溶媒に溶解してフィルム状に形成する工程を有し、かつ前記原料となる高分子量体を有機溶媒の溶解前に減圧乾燥をすることを特徴とする有機圧電材料の製造方法。 6. 6. The method for producing an organic piezoelectric material according to any one of 1 to 5, comprising a step of dissolving a high molecular weight material, which is a raw material of the organic piezoelectric material, in an organic solvent to form a film. And the high molecular weight body used as the said raw material is dried under reduced pressure before melt | dissolution of an organic solvent, The manufacturing method of the organic piezoelectric material characterized by the above-mentioned.
　７．前記１～５のいずれか１項に記載の有機圧電材料を用いることを特徴とする超音波振動子。 7. 6. An ultrasonic transducer using the organic piezoelectric material according to any one of 1 to 5 above.
　８．電気信号を発生する手段と、前記電気信号を受けて超音波を被検体に向けて送信し、前記被検体から受けた反射波に応じた受信信号を生成する複数の振動子が配置された超音波探触子と、前記超音波探触子が生成した前記受信信号に応じて、前記被検体の画像を生成する画像処理手段とを有する超音波医用画像診断装置において、前記超音波探触子が、送信用超音波振動子と受信用超音波振動子の両方を具備し、かつ、該超音波振動子のどちらか一方もしくは両方が前記７に記載の超音波振動子であることを特徴とする超音波医用画像診断装置。 8. Ultrasound in which a means for generating an electrical signal and a plurality of transducers for receiving the electrical signal and transmitting an ultrasonic wave toward the subject and generating a reception signal corresponding to the reflected wave received from the subject are arranged In the ultrasonic medical image diagnostic apparatus, comprising: an ultrasonic probe; and an image processing unit that generates an image of the subject according to the reception signal generated by the ultrasonic probe. Comprising both a transmitting ultrasonic transducer and a receiving ultrasonic transducer, and one or both of the ultrasonic transducers is the ultrasonic transducer according to 7 above, Ultrasonic medical diagnostic imaging device.
　本発明の上記手段により、圧電特性及び耐熱性に優れ、かつ高周波・広帯域に適した超音波振動子を構成するための有機圧電材料、その製造方法、それを用いた超音波探触子、及び超音波医用画像診断装置を提供することができる。 By the above-described means of the present invention, an organic piezoelectric material that is excellent in piezoelectric characteristics and heat resistance and that is suitable for high frequency and wide band, an organic piezoelectric material for manufacturing the same, an ultrasonic probe using the same, and An ultrasonic medical image diagnostic apparatus can be provided.
試料１（本発明）と試料３（比較）の残留分極量のヒステリシス曲線である。It is a hysteresis curve of the amount of remanent polarization of sample 1 (the present invention) and sample 3 (comparison). 試料１（本発明）と試料３（比較）の電気機械結合定数の時間経過グラフである。It is a time course graph of the electromechanical coupling constant of the sample 1 (this invention) and the sample 3 (comparison).
　本発明を更に詳しく説明する。 The present invention will be described in more detail.
　本発明の超音波振動子は、超音波医用画像診断装置用探触子に用いられる超音波圧電材料を有する超音波振動子であって、当該超音波圧電材料がフッ化ビニリデンを主成分とする有機圧電材料であり、当該有機圧電材料単位質量あたりに含まれる残モノマー量が２００ｐｐｍ以下であり、この特徴は、請求の範囲１～５に係る発明に共通する技術的特徴である。 The ultrasonic transducer of the present invention is an ultrasonic transducer having an ultrasonic piezoelectric material used for a probe for an ultrasonic medical diagnostic imaging apparatus, and the ultrasonic piezoelectric material is mainly composed of vinylidene fluoride. It is an organic piezoelectric material, and the amount of residual monomer contained per unit mass of the organic piezoelectric material is 200 ppm or less, and this feature is a technical feature common to the inventions according to claims 1 to 5.
　なお、本発明の実施形態・態様としては、圧電特性の観点から、前記有機圧電材料が延伸製膜されていることが好ましい。 As an embodiment / mode of the present invention, it is preferable that the organic piezoelectric material is stretched and formed from the viewpoint of piezoelectric characteristics.
　本発明の超音波振動子の製造方法としては、有機圧電体膜の両面に設置される電極の形成前、片側のみ電極形成後又は両側に電極形成後のいずれかで分極処理する態様の製造方法であることが好ましい。また、当該分極処理が、電圧印加処理であることが好ましい。 As a method for manufacturing the ultrasonic vibrator of the present invention, a method for manufacturing an aspect in which polarization treatment is performed either before forming electrodes to be installed on both sides of an organic piezoelectric film, after forming electrodes on only one side, or after forming electrodes on both sides. It is preferable that Moreover, it is preferable that the said polarization process is a voltage application process.
　本発明の超音波振動子は、他の超音波振動子と組み合わせて超音波探触子を構成することができる。この場合当該超音波探触子が、本発明の超音波振動子と同種の有機圧電材料、或いは別の既知の圧電材料でもよく、該圧電材料は無機材料でも高分子材料でもよく、更に組み合わされる材料は圧電材料ではない別の高分子材料でもよい。当該超音波探触子は、上記材料が貼り合わされて構成される２層以上の積層振動子であり、かつ当該積層振動子の厚さが、２０～６００μｍである態様とすることが好ましい。 The ultrasonic transducer of the present invention can be combined with other ultrasonic transducers to constitute an ultrasonic probe. In this case, the ultrasonic probe may be an organic piezoelectric material of the same type as the ultrasonic transducer of the present invention, or another known piezoelectric material, and the piezoelectric material may be an inorganic material or a polymer material, and further combined. The material may be another polymeric material that is not a piezoelectric material. The ultrasonic probe is preferably a laminated vibrator having two or more layers formed by bonding the above materials, and the laminated vibrator has a thickness of 20 to 600 μm.
　本発明の超音波振動子若しくはそれを用いた超音波探触子は、超音波医用画像診断装置に好適に使用することができる。 The ultrasonic transducer of the present invention or an ultrasonic probe using the ultrasonic transducer can be suitably used for an ultrasonic medical image diagnostic apparatus.
　以下、本発明とその構成要素、及び本発明を実施するための最良の形態・態様について詳細な説明をする。 Hereinafter, the present invention, its components, and the best mode and mode for carrying out the present invention will be described in detail.
　（超音波振動子）
　本発明の超音波振動子は、超音波送信用振動子と超音波受信用振動子とを具備する超音波医用画像診断装置用探触子（プローブ）に用いられることを特徴とする。 (Ultrasonic transducer)
The ultrasonic transducer according to the present invention is used for a probe for an ultrasonic medical diagnostic imaging apparatus including an ultrasonic transmission transducer and an ultrasonic reception transducer.
　一般に、超音波振動子は膜状の圧電材料からなる層（又は膜）（以下、圧電体層」又は「圧電体膜」という。）を挟んで一対の電極を配設して構成され、複数の振動子を例えば１次元配列して超音波探触子が構成される。 In general, an ultrasonic transducer is configured by arranging a pair of electrodes with a layer (or film) (hereinafter referred to as a piezoelectric layer) or a “piezoelectric film” made of a film-like piezoelectric material in between. For example, an ultrasonic probe is configured by one-dimensionally arranging the transducers.
　そして、複数の振動子が配列された長軸方向の所定数の振動子を口径として設定し、その口径に属する複数の振動子を駆動して被検体内の計測部位に超音波ビームを収束させて照射すると共に、その口径に属する複数の振動子により被検体から発する超音波の反射エコー等を受信して電気信号に変換する機能を有している。 Then, a predetermined number of transducers in the major axis direction in which a plurality of transducers are arranged is set as the aperture, and the plurality of transducers belonging to the aperture are driven to converge the ultrasonic beam on the measurement site in the subject. And has a function of receiving reflected echoes of ultrasonic waves emitted from the subject by a plurality of transducers belonging to the aperture and converting them into electrical signals.
　（有機圧電材料）
　本発明の超音波振動子を構成する圧電材料の構成材料としての有機圧電材料としては低分子材料、高分子材料を問わず採用でき、低分子の有機圧電材料であれば、例えば、フタル酸エステル系化合物、スルフェンアミド系化合物、フェノール骨格を有する有機化合物などが挙げられる。高分子の有機圧電材料であれば、例えば、ポリフッ化ビニリデン、あるいはポリフッ化ビニリデン系共重合体、ポリシアン化ビニリデンあるいはシアン化ビニリデン系共重合体あるはナイロン９、ナイロン１１などの奇数ナイロンや、芳香族ナイロン、脂環族ナイロン、あるいはポリ乳酸や、ポリヒドロキシブチレートなどのポリヒドロキシカルボン酸、セルロース系誘導体、ポリウレアなどが挙げられる。良好な圧電特性、加工性、入手容易性等の観点から、高分子の有機圧電材料、特にフッ化ビニリデンを主成分とする高分子材料であることを要する。 (Organic piezoelectric material)
The organic piezoelectric material as the constituent material of the piezoelectric material constituting the ultrasonic vibrator of the present invention can be adopted regardless of whether it is a low molecular material or a high molecular material. Compounds, sulfenamide compounds, organic compounds having a phenol skeleton, and the like. In the case of a high molecular organic piezoelectric material, for example, polyvinylidene fluoride, a polyvinylidene fluoride copolymer, a polyvinylidene cyanide or a vinylidene cyanide copolymer, an odd-numbered nylon such as nylon 9 or nylon 11, or an aromatic Aromatic nylon, alicyclic nylon, polylactic acid, polyhydroxycarboxylic acids such as polyhydroxybutyrate, cellulose derivatives, polyurea and the like. From the viewpoint of good piezoelectric properties, processability, availability, etc., it is necessary to be a polymer organic piezoelectric material, particularly a polymer material mainly composed of vinylidene fluoride.
　具体的には、大きい双極子モーメントをもつＣＦ２基を有する、ポリフッ化ビニリデンの単独重合体又はフッ化ビニリデンを主成分とする共重合体であることを要する。なお、共重合体における第二組成分としては、テトラフルオロエチレン、トリフルオロエチレン、ヘキサフルオロプロパン、クロロフルオロエチレン等を用いることができる。 Specifically, it is necessary to be a homopolymer of polyvinylidene fluoride having a CF 2 group having a large dipole moment or a copolymer having vinylidene fluoride as a main component. In addition, tetrafluoroethylene, trifluoroethylene, hexafluoropropane, chlorofluoroethylene, etc. can be used as the second component in the copolymer.
　例えば、フッ化ビニリデン／３フッ化エチレン共重合体の場合、共重合比によって厚さ方向の電気機械結合定数（圧電効果）が変化すので、前者の共重合比が６０～９９モル％であるこ、更には、８５～９９モル％であることが好ましい。 For example, in the case of vinylidene fluoride / trifluoroethylene copolymer, the electromechanical coupling constant (piezoelectric effect) in the thickness direction varies depending on the copolymerization ratio, so that the former copolymerization ratio is 60 to 99 mol%. Further, it is preferably 85 to 99 mol%.
　なお、フッ化ビニリデンを８５～９９モル％にして、パーフルオロアルキルビニルエーテル、パーフルオロアルコキシエチレン、パーフルオロヘキサエチレン等を１～１５モル％にしたポリマーは、送信用無機圧電素子と受信用有機圧電素子との組み合わせにおいて、送信基本波を抑制して、高調波受信の感度を高めることができる。 A polymer containing 85 to 99 mol% of vinylidene fluoride and 1 to 15 mol% of perfluoroalkyl vinyl ether, perfluoroalkoxyethylene, perfluorohexaethylene, etc. is composed of an inorganic piezoelectric element for transmission and an organic piezoelectric element for reception. In combination with the element, it is possible to suppress the transmission fundamental wave and increase the sensitivity of harmonic reception.
　上記有機圧電材料は、セラミックスからなる無機圧電材料に比べ、薄膜化できることからより高周波の送受信に対応した振動子にすることができる点が特徴である。 Since the organic piezoelectric material can be made thinner than an inorganic piezoelectric material made of ceramics, the organic piezoelectric material is characterized in that it can be used as a vibrator corresponding to transmission and reception of higher frequencies.
　本発明においては、当該有機圧電材料は、厚み共振周波数における比誘電率が１０～５０であることを特徴とするが、比誘電率の調整は、当該有機圧電材料を構成する化合物が有するＣＦ２基やＣＮ基のような極性官能基の数量、組成、重合度等の調整、及び後述する分極処理によって行うことができる。 In the present invention, the organic piezoelectric material has a relative dielectric constant of 10 to 50 at a thickness resonance frequency. Adjustment of the relative dielectric constant is performed by CF 2 contained in a compound constituting the organic piezoelectric material. It can be carried out by adjusting the quantity, composition, degree of polymerization, etc. of polar functional groups such as groups and CN groups, and polarization treatment described later.
　なお、本発明の振動子を構成する有機圧電体膜は、複数の高分子材料を積層させた構成とすることもできる。この場合、積層する高分子材料としては、上記の高分子材料の他に下記の比誘電率の比較的低い高分子材料を併用することができる。 It should be noted that the organic piezoelectric film constituting the vibrator of the present invention may be configured by laminating a plurality of polymer materials. In this case, as the polymer material to be laminated, the following polymer material having a relatively low relative dielectric constant can be used in addition to the above polymer material.
　なお、下記の例示において、括弧内の数値は、高分子材料（樹脂）の比誘電率を示す。例えば、メタクリル酸メチル樹脂（３．０）、アクリルニトリル樹脂（４．０）、アセテート樹脂（３．４）、アニリン樹脂（３．５）、アニリンホルムアルデヒド樹脂（４．０）、アミノアルキル樹脂（４．０）、アルキッド樹脂（５．０）、ナイロン－６－６（３．４）、エチレン樹脂（２．２）、エポキシ樹脂（２．５）、塩化ビニル樹脂（３．３）、塩化ビニリデン樹脂（３．０）、尿素ホルムアルデヒド樹脂（７．０）、ポリアセタール樹脂（３．６）、ポリウレタン（５．０）、ポリエステル樹脂（２．８）、ポリエチレン（低圧）（２．３）、ポリエチレンテレフタレート（２．９）、ポリカーポネート樹脂（２．９）、メラミン樹脂（５．１）、メラミンホルムアルデヒド樹脂（８．０）、酢酸セルロース（３．２）、酢酸ビニル樹脂（２．７）、スチレン樹脂（２．３）、スチレンブタジェンゴム（３．０）、スチロール樹脂（２．４）、フッ化エチレン樹脂（２．０）等を用いることができる。 In the following examples, the numerical value in parentheses indicates the relative dielectric constant of the polymer material (resin). For example, methyl methacrylate resin (3.0), acrylonitrile resin (4.0), acetate resin (3.4), aniline resin (3.5), aniline formaldehyde resin (4.0), aminoalkyl resin ( 4.0), alkyd resin (5.0), nylon-6-6 (3.4), ethylene resin (2.2), epoxy resin (2.5), vinyl chloride resin (3.3), chloride Vinylidene resin (3.0), urea formaldehyde resin (7.0), polyacetal resin (3.6), polyurethane (5.0), polyester resin (2.8), polyethylene (low pressure) (2.3), Polyethylene terephthalate (2.9), polycarbonate resin (2.9), melamine resin (5.1), melamine formaldehyde resin (8.0), cellulose acetate (3.2), acetic acid Sulfonyl resin (2.7), styrene resins (2.3), styrene butadiene rubber (3.0), styrene resin (2.4), it can be used polytetrafluoroethylene (2.0) or the like.
　なお、上記比誘電率の低い高分子材料は、圧電特性を調整するため、或いは有機圧電体膜の物理的強度を付与するため等の種々の目的に応じて適切なものを選択することが好ましい。 The polymer material having a low relative dielectric constant is preferably selected in accordance with various purposes such as adjusting the piezoelectric characteristics or imparting the physical strength of the organic piezoelectric film. .
　本発明における有機圧電材料に含まれる残留モノマーは、高分子材料を重合工程により作製する際に未転化であった微量の低分子モノマーである。残留モノマーを減らすには、いくつかの一般的手段が用いることができる。例えば、重合終了直前に系に新たに開始剤などのラジカル生成種を加える、重合終了後に洗浄工程を用いて生成物と未反応物を分離する、低分子モノマーが揮発性であれば、温度や減圧下において分離するなどがあげられる。本発明における有機圧電材料においては、残留モノマー量が多いと分極処理中に低分子モノマーを介して絶縁破壊が極めて起こりやすく、また保存時の分子運動を促進するため圧電性能の低下が引き起こされてしまう。 The residual monomer contained in the organic piezoelectric material in the present invention is a small amount of low molecular weight monomer that has not been converted when the polymer material is produced by the polymerization process. Several common means can be used to reduce residual monomer. For example, a radical generating species such as an initiator is newly added to the system immediately before the end of polymerization, and a product and unreacted substances are separated using a washing process after the end of polymerization. Separation under reduced pressure, and the like. In the organic piezoelectric material of the present invention, if the amount of residual monomer is large, dielectric breakdown is very likely to occur through the low-molecular monomer during the polarization treatment, and the piezoelectric performance is reduced because the molecular motion during storage is promoted. End up.
　（有機圧電体膜の作製方法）
　本発明に係る有機圧電体膜は、上記高分子材料を主たる構成成分として種々の方法で作製することができる。 (Method for producing organic piezoelectric film)
The organic piezoelectric film according to the present invention can be produced by various methods using the polymer material as a main constituent.
　有機圧電体膜の作製方法としては、基本的には、上記高分子材料の溶液を基板上に塗布し、乾燥して得る方法、又は上記高分子材料の原料化合物を用いて従来公知の蒸着重合法や溶液重合塗布法などにより高分子膜を形成する方法を採用することができる。 As a method for producing an organic piezoelectric film, basically, a solution obtained by applying a solution of the polymer material on a substrate and drying it, or a conventionally known vapor deposition weight using a raw material compound of the polymer material is used. A method of forming a polymer film by a combination method, a solution polymerization coating method, or the like can be employed.
　蒸着重合法の具体的方法・条件については、特開平７－２５８３７０号公報、特開平５－３１１３９９号公報、及び特開２００６－４９４１８号公報に開示されている方法等が参考となる。 For specific methods and conditions of the vapor deposition polymerization method, the methods disclosed in JP-A-7-258370, JP-A-5-311399, and JP-A-2006-49418 can be referred to.
　溶液重合塗布法の具体的方法・条件については、従来公知の種々の方法等に従って行うことができる。例えば、原料の混合溶液を基板上に塗布し、減圧条件下である程度乾燥後（溶媒を除去した後）、加熱し、熱重合し、その後又は同時に分極処理をして有機圧電体膜を形成する方法が好ましい。 The specific method and conditions of the solution polymerization coating method can be performed according to various conventionally known methods. For example, a mixed solution of raw materials is applied onto a substrate, dried to some extent under reduced pressure conditions (after the solvent is removed), heated, thermally polymerized, and then or simultaneously polarized to form an organic piezoelectric film. The method is preferred.
　（延伸製膜）
　本発明に係るフッ化ビニリデンを含む有機圧電材料を振動子とする場合、フィルム状に形成し、ついで電気信号を入力するための表面電極を形成するのが一般的である。 (Stretched film formation)
When the organic piezoelectric material containing vinylidene fluoride according to the present invention is used as a vibrator, it is generally formed in a film shape and then a surface electrode for inputting an electric signal.
　フィルム形成は、溶融法、流延法など一般的な方法を用いることができる。ポリフッ化ビニリデン－トリフルオロエチレン共重合体の場合、フィルム状にしたのみで自発分極をもつ結晶型を有することが知られているが、さらに特性を上げるには、分子配列を揃える処理を加えることが有用である。手段としては、延伸製膜、分極処理などが挙げられる。 For film formation, a general method such as a melting method or a casting method can be used. In the case of a polyvinylidene fluoride-trifluoroethylene copolymer, it is known that it has a crystalline form with spontaneous polarization only when it is made into a film, but in order to further improve the characteristics, a process for aligning the molecular arrangement should be added. Is useful. Examples of means include stretching film formation and polarization treatment.
　延伸製膜の方法については、種々の公知の方法を採用することができる。例えば、上記高分子材料をエチルメチルケトン（ＭＥＫ）などの有機溶媒に溶解した液をガラス板などの基板上に流延し、常温にて溶媒を乾燥させ、所望の厚さのフィルムを得て、このフィルムを室温で所定の倍率の長さに延伸する。当該延伸は、所定形状の有機圧電体膜が破壊されない程度に一軸・ニ軸方向に延伸することができる。延伸倍率は２～１０倍、好ましくは２～６倍である。 As the stretching film forming method, various known methods can be employed. For example, a solution obtained by dissolving the above polymer material in an organic solvent such as ethyl methyl ketone (MEK) is cast on a substrate such as a glass plate, and the solvent is dried at room temperature to obtain a film having a desired thickness. The film is stretched to a predetermined length at room temperature. The stretching can be performed in a uniaxial / biaxial direction so that the organic piezoelectric film having a predetermined shape is not broken. The draw ratio is 2 to 10 times, preferably 2 to 6 times.
　なお、フッ化ビニリデン－トリフルオロエチレン共重合体および／またはフッ化ビニリデン－テトラフルオロエチレン共重合体において、２３０℃における溶融流動速度（Ｍｅｌｔ　Ｆｌｏｗ　Ｒａｔｅ）が０．０３ｇ／ｍｉｎ以下である。より好ましくは、０．０２ｇ／ｍｉｎ以下、更に好ましくは、０．０１ｇ／ｍｉｎ以下である高分子圧電体を使用すると高感度な圧電体の薄膜が得られる。 Incidentally, in the vinylidene fluoride-trifluoroethylene copolymer and / or the vinylidene fluoride-tetrafluoroethylene copolymer, the melt flow rate at 230 ° C. (Melt Flow Rate) is 0.03 g / min or less. More preferably, a high-sensitivity piezoelectric thin film can be obtained by using a polymer piezoelectric material of 0.02 g / min or less, more preferably 0.01 g / min or less.
　（分極処理）
　本発明に係る分極処理における分極処理方法としては、従来公知の直流電圧印加処理、交流電圧印加処理又はコロナ放電処理等の方法が適用され得る。 (Polarization treatment)
As a polarization treatment method in the polarization treatment according to the present invention, a conventionally known method such as DC voltage application treatment, AC voltage application treatment, or corona discharge treatment can be applied.
　例えば、コロナ放電処理法による場合には、コロナ放電処理は、市販の高電圧電源と電極からなる装置を使用して処理することができる。 For example, in the case of the corona discharge treatment method, the corona discharge treatment can be performed by using a commercially available apparatus comprising a high voltage power source and electrodes.
　放電条件は、機器や処理環境により異なるので適宜条件を選択することが好ましい。高電圧電源の電圧としては－１～－２０ｋＶ、電流としては１～８０ｍＡ、電極間距離としては、１～１０ｃｍが好ましく、印加電圧は、０．５～２．０ＭＶ／ｍであることが好ましい。 Since the discharge conditions vary depending on the equipment and the processing environment, it is preferable to select the conditions appropriately. The voltage of the high voltage power source is preferably −1 to −20 kV, the current is 1 to 80 mA, the distance between the electrodes is preferably 1 to 10 cm, and the applied voltage is preferably 0.5 to 2.0 MV / m. .
　電極としては、従来から用いられている針状電極、線状電極（ワイヤー電極）、網状電極が好ましいが、本発明ではこれらに限定されるものではない。 As the electrodes, needle-like electrodes, linear electrodes (wire electrodes), and mesh electrodes conventionally used are preferable, but the invention is not limited thereto.
　（基板）
　基板としては、本発明に係る有機圧電体膜の用途・使用方法等により基板の選択は異なる。本発明においては、ポリイミド、ポリアミド、ポリイミドアミド、ポリエチレンテレフタラート（ＰＥＴ）、ポリエチレンナフタレート（ＰＥＮ）、ポリメタクリル酸メチル（ＰＭＭＡ）、ポリカーボネート樹脂、シクロオレフィンポリマーのようなプラスチック板又はフィルムを用いることができる。また、これらの素材の表面をアルミニウム、金、銅、マグネシウム、珪素等で覆ったものでもよい。またアルミニウム、金、銅、マグネシウム、珪素単体、希土類のハロゲン化物の単結晶の板又はフィルムでもかまわない。 (substrate)
As the substrate, the selection of the substrate differs depending on the application and use method of the organic piezoelectric film according to the present invention. In the present invention, a plastic plate or film such as polyimide, polyamide, polyimide amide, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polymethyl methacrylate (PMMA), polycarbonate resin, or cycloolefin polymer is used. Can do. Further, the surface of these materials may be covered with aluminum, gold, copper, magnesium, silicon or the like. Alternatively, a single crystal plate or film of aluminum, gold, copper, magnesium, silicon alone, or a rare earth halide may be used.
　（電極）
　本発明に係る圧電材料を有する振動子は、圧電体膜（層）の両面上又は片面上に電極を形成し、その圧電体膜を分極処理することによって作製されるものである。当該電極は、金（Ａｕ）、白金（Ｐｔ）、銀（Ａｇ）、パラジウム（Ｐｄ）、銅（Ｃｕ）、ニッケル（Ｎｉ）、スズ（Ｓｎ）などを主体とした電極材料を用いて形成する。 (electrode)
The vibrator having the piezoelectric material according to the present invention is manufactured by forming electrodes on both surfaces or one surface of a piezoelectric film (layer) and polarizing the piezoelectric film. The electrode is formed using an electrode material mainly composed of gold (Au), platinum (Pt), silver (Ag), palladium (Pd), copper (Cu), nickel (Ni), tin (Sn), or the like. .
　電極の形成に際しては、まず、チタン（Ｔｉ）やクロム（Ｃｒ）などの下地金属をスパッタ法により０．０２～１．０μｍの厚さに形成する。その後、上記金属元素を主体とする金属及びそれらの合金からなる金属材料、さらには必要に応じ一部絶縁材料をスパッタ法、その他の適当な方法で１～１０μｍの厚さに形成する。これらの電極形成はスパッタ法以外でも微粉末の金属粉末と低融点ガラスを混合した導電ペーストをスクリーン印刷やディッピング法、溶射法で形成することもできる。 When forming the electrode, first, a base metal such as titanium (Ti) or chromium (Cr) is formed to a thickness of 0.02 to 1.0 μm by sputtering. Thereafter, a metal material mainly composed of the above metal element and a metal material thereof, and further, if necessary, a part of insulating material is formed to a thickness of 1 to 10 μm by sputtering or other suitable methods. In addition to sputtering, these electrodes can be formed by screen printing, dipping, or thermal spraying using a conductive paste in which fine metal powder and low-melting glass are mixed.
　さらに、圧電体膜の両面に形成した電極間に、所定の電圧を供給し、圧電体膜を分極することで圧電素子が得られる。 Furthermore, a piezoelectric element can be obtained by supplying a predetermined voltage between the electrodes formed on both surfaces of the piezoelectric film to polarize the piezoelectric film.
　（超音波探触子）
　本発明に係る超音波探触子は、超音波送信用振動子と超音波受信用振動子を具備する超音波医用画像診断装置用探触子（プローブ）であり、本発明の上記超音波受信用振動子を用いることを特徴とする。 (Ultrasonic probe)
An ultrasonic probe according to the present invention is a probe for an ultrasonic medical diagnostic imaging apparatus including an ultrasonic transmission transducer and an ultrasonic reception transducer, and the ultrasonic reception according to the present invention. A vibrator is used.
　本発明においては、超音波の送受信の両方をひとつの振動子で担ってもよいが、より好ましくは、送信用と受信用で振動子は分けて探触子内に構成される。 In the present invention, both the transmission and reception of ultrasonic waves may be performed by a single transducer, but more preferably, the transducer is configured separately for transmission and reception in the probe.
　送信用振動子を構成する圧電材料としては、従来公知のセラミックス無機圧電材料でも、有機圧電材料でもよい。 The piezoelectric material constituting the transmitting vibrator may be a conventionally known ceramic inorganic piezoelectric material or an organic piezoelectric material.
　本発明に係る超音波探触子においては、送信用振動子の上もしくは並列に本発明の超音波受信用振動子を配置することができる。 In the ultrasonic probe according to the present invention, the ultrasonic receiving transducer of the present invention can be arranged on or in parallel with the transmitting transducer.
　より好ましい実施形態としては、超音波送信用振動子の上に本発明の超音波受信用振動子を積層する構造が良く、その際には、本発明の超音波受信用振動子は他の高分子材料（支持体として上記の比誘電率が比較的低い高分子（樹脂）フィルム、例えば、ポリエステルフィルム）の上に添合した形で送信用振動子の上に積層してもよい。その際の受信用振動子と他の高分子材料と合わせた膜厚は、探触子の設計上好ましい受信周波数帯域に合わせることが好ましい。実用的な超音波医用画像診断装置および生体情報収集に現実的な周波数帯から鑑みると、その膜厚は、４０～１５０μｍであることが好ましい。 As a more preferred embodiment, the structure for laminating the ultrasonic receiving transducer of the present invention on the ultrasonic transmitting transducer is good, and in this case, the ultrasonic receiving transducer of the present invention is another high-frequency transducer. You may laminate | stack on the vibrator | oscillator for transmission in the form joined together on the molecular material (The polymer (resin) film, for example, polyester film) whose relative dielectric constant is comparatively low as a support body. In this case, it is preferable that the film thickness of the receiving vibrator and the other polymer material be matched to a preferable receiving frequency band in terms of probe design. In view of a practical ultrasonic medical image diagnostic apparatus and biological information collection from a practical frequency band, the film thickness is preferably 40 to 150 μm.
　なお、当該探触子には、バッキング層、音響整合層、音響レンズなどを設けても良い。また、多数の圧電材料を有する振動子を２次元に並べた探触子とすることもできる。複数の２次元配列した探触子を順次走査して、画像化するスキャナーとして構成させることもできる。 The probe may be provided with a backing layer, an acoustic matching layer, an acoustic lens, and the like. Also, a probe in which vibrators having a large number of piezoelectric materials are two-dimensionally arranged can be used. A plurality of two-dimensionally arranged probes can be sequentially scanned to form a scanner.
　（超音波医用画像診断装置）
　本発明に係る上記超音波探触子は、種々の態様の超音波診断装置に用いることができる。例えば、患者などの被検体に対して超音波を送信し、被検体で反射した超音波をエコー信号として受信する圧電体体振動子が配列されている超音波探触子（プローブ）を備えている超音波医用画像診断装置が好ましい。また当該超音波探触子に電気信号を供給して超音波を発生させるとともに、当該超音波探触子の各圧電体振動子が受信したエコー信号を受信する送受信回路と、送受信回路の送受信制御を行う送受信制御回路を備えていることが好ましい。 (Ultrasonic medical diagnostic imaging equipment)
The ultrasonic probe according to the present invention can be used for various types of ultrasonic diagnostic apparatuses. For example, an ultrasonic probe (probe) in which piezoelectric body transducers that transmit ultrasonic waves to a subject such as a patient and receive ultrasonic waves reflected from the subject as echo signals is arranged is provided. An ultrasonic medical diagnostic imaging apparatus is preferred. In addition, an electric signal is supplied to the ultrasonic probe to generate an ultrasonic wave, and a transmission / reception circuit that receives an echo signal received by each piezoelectric vibrator of the ultrasonic probe, and transmission / reception control of the transmission / reception circuit It is preferable that a transmission / reception control circuit for performing the above is provided.
　更に、送受信回路が受信したエコー信号を被検体の超音波画像データに変換する画像データ変換回路を備え、当該画像データ変換回路によって変換された超音波画像データでモニタを制御して表示する表示制御回路と、超音波医用画像診断装置全体の制御を行う制御回路を備えた超音波医用画像診断装置が好ましい。 Further, the display control unit includes an image data conversion circuit that converts the echo signal received by the transmission / reception circuit into ultrasonic image data of the subject, and controls and displays the monitor with the ultrasonic image data converted by the image data conversion circuit. An ultrasonic medical image diagnostic apparatus including a circuit and a control circuit that controls the entire ultrasonic medical image diagnostic apparatus is preferable.
　このような超音波医用画像診断装置は、制御回路には、送受信制御回路、画像データ変換回路、表示制御回路が接続されており、制御回路はこれら各部の動作を制御している。そして、超音波探触子の各圧電体振動子に電気信号を印加して被検体に対して超音波を送信し、被検体内部で音響インピーダンスの不整合によって生じる反射波を超音波探触子で受信する。 In such an ultrasonic medical image diagnostic apparatus, a transmission / reception control circuit, an image data conversion circuit, and a display control circuit are connected to a control circuit, and the control circuit controls operations of these units. Then, an electrical signal is applied to each piezoelectric vibrator of the ultrasonic probe to transmit an ultrasonic wave to the subject, and the reflected wave caused by acoustic impedance mismatch inside the subject is detected by the ultrasonic probe. Receive at.
　なお、上記送受信回路が「電気信号を発生する手段」に相当し、画像データ変換回路が「画像処理手段」に相当する。 The transmission / reception circuit corresponds to “means for generating an electric signal”, and the image data conversion circuit corresponds to “image processing means”.
　上記のような超音波診断装置によれば、本発明の圧電特性及び耐熱性に優れかつ高周波・広帯域に適した超音波受信用振動子の特徴を生かして、従来技術と比較して画質とその再現・安定性が向上した超音波像を得ることができる。 According to the ultrasonic diagnostic apparatus as described above, by utilizing the characteristics of the ultrasonic wave receiving vibrator excellent in piezoelectric characteristics and heat resistance of the present invention and suitable for high frequency and wide band, the image quality and its An ultrasonic image with improved reproduction and stability can be obtained.
　以下、実施例を挙げて本発明を説明するが、本発明はこれらに限定されない。 Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto.
　（有機圧電体膜の作製と評価）
　実施例１
　フッ化ビニリデン（以下ＶＤＦ）とトリフルオロエチレン（以下３ＦＥ）のモル比率が７５：２５であるポリフッ化ビニリデン共重合体粉末（重量平均分子量２９万）を減圧オーブンにて５０℃で１２時間乾燥させた。ついで、この粉体を５０℃に加熱したエチルメチルケトン（以下ＭＥＫ）、ジメチルホルムアミド（以下ＤＭＦ）の９：１混合溶媒に溶解した液をガラス板上に流延した。その後、５０℃にて溶媒を乾燥させ、厚さ約１４０μｍのフィルム（有機圧電体膜）を得た。このフィルムを室温で４倍に延伸した後、延伸した長さを保ったまま１３５℃１時間熱処理を行った。得られた熱処理後のフィルムの膜厚は４３μｍであった。 (Production and evaluation of organic piezoelectric film)
Example 1
Polyvinylidene fluoride copolymer powder (weight average molecular weight 290,000) having a molar ratio of vinylidene fluoride (hereinafter VDF) and trifluoroethylene (hereinafter 3FE) of 75:25 is dried at 50 ° C. for 12 hours in a vacuum oven. It was. Next, a solution of this powder in a 9: 1 mixed solvent of ethyl methyl ketone (hereinafter referred to as MEK) and dimethylformamide (hereinafter referred to as DMF) heated to 50 ° C. was cast on a glass plate. Thereafter, the solvent was dried at 50 ° C. to obtain a film (organic piezoelectric film) having a thickness of about 140 μm. This film was stretched 4 times at room temperature, and then heat treated at 135 ° C. for 1 hour while maintaining the stretched length. The film thickness after heat treatment was 43 μm.
　ここで得られたフィルムの両面に表面抵抗が２０Ω以下になるように金／アルミニウムを蒸着塗布して表面電極付の試料を得た。 A sample with a surface electrode was obtained by vapor-depositing gold / aluminum on both surfaces of the film obtained here so that the surface resistance was 20Ω or less.
　つづいて、この電極に室温にて、０．１Ｈｚの交流電圧を印可しながら分極処理を行った。分極処理は低電圧から行い、最終的に電極間電場が１００ＭＶ／ｍになるまで徐々に電圧をかけていった。最終的な分極量は、圧電材料をコンデンサと見たてた際の残留分極量、すなわち膜厚、電極面積、印可電場に対する電荷蓄積量から求め、本発明の試料１を得た。 Subsequently, the electrode was subjected to polarization treatment while applying an AC voltage of 0.1 Hz at room temperature. The polarization treatment was performed from a low voltage, and the voltage was gradually applied until the electric field between the electrodes finally reached 100 MV / m. The final polarization amount was obtained from the residual polarization amount when the piezoelectric material was regarded as a capacitor, that is, the film thickness, the electrode area, and the charge accumulation amount with respect to the applied electric field, and Sample 1 of the present invention was obtained.
　本発明の試料２、５、７及び比較の試料３、４、６については、表１に示す乾燥条件でポリフッ化ビニリデン共重合体粉末を乾燥した以外は試料１同様に製膜、電極付けを行って分極済の試料２～７を得た。 For Samples 2, 5, and 7 of the present invention and Comparative Samples 3, 4, and 6, film formation and electrode attachment were performed in the same manner as Sample 1 except that the polyvinylidene fluoride copolymer powder was dried under the drying conditions shown in Table 1. To obtain polarized samples 2-7.
　［残留モノマー量］
　分極する前のフィルム０．３ｇを専用バイアル瓶に収納しセプタムとアルミキャップで密閉した後、ヘッドスペースサンプラーと接続したガスクロマトグラフィー（ＧＣ）を用いて測定した。検出器として水素炎イオン化検出器（ＦＩＤ）を用いた。主な測定条件として、ヘッドスペースサンプラー加熱条件：１００℃、２０分であり、ＧＣ導入温度：１１０℃、カラム昇温条件：５０℃の状態から毎分５℃上昇で１００℃とした。測定対象一定量を専用バイアル瓶に加圧収納した後、得られたクロマトグラムのピーク面積を用いて作製した検量線を使用して試料中の残留モノマー量を得た。 [Residual monomer amount]
0.3 g of the film before polarization was housed in a special vial, sealed with a septum and an aluminum cap, and then measured using a gas chromatography (GC) connected to a headspace sampler. A flame ionization detector (FID) was used as a detector. The main measurement conditions were head space sampler heating conditions: 100 ° C., 20 minutes, GC introduction temperature: 110 ° C., column heating conditions: 50 ° C., and increased to 5 ° C. per minute to 100 ° C. After a certain amount of the measurement object was pressure-stored in a dedicated vial, the amount of residual monomer in the sample was obtained using a calibration curve prepared using the peak area of the obtained chromatogram.
　［電極耐久性］
　［有機圧電体膜の評価方法］
　上記のようにして得られた電極付の試料の両面の電極にリード線を付け、アジレントテクノロジー社製インピーダンスアナライザ４２９４Ａを用いて、２５℃雰囲気下において、４０Ｈｚから１１０ＭＨｚまで等間隔で６００点周波数掃引した。厚み共振周波数における比誘電率の値を求めた。同様に、厚み共振周波数付近の抵抗値のピーク周波数Ｐ、コンダクタンスのピーク周波数Ｓをそれぞれ求めたとき、下記式にて電気機械結合定数ｋｔを求めた。 [Electrode durability]
[Method for evaluating organic piezoelectric film]
Lead wires are attached to the electrodes on both sides of the sample with the electrode obtained as described above, and frequency scanning is performed at 600 points at equal intervals from 40 Hz to 110 MHz in an atmosphere of 25 ° C. using an impedance analyzer 4294A manufactured by Agilent Technologies. did. The value of the relative dielectric constant at the thickness resonance frequency was obtained. Similarly, when the peak frequency P of the resistance value near the thickness resonance frequency and the peak frequency S of the conductance were obtained, the electromechanical coupling constant kt was obtained by the following equation .
　ｋｔ＝（α／ｔａｎ（α））１／２　ただし、α＝（π／２）×（Ｓ／Ｐ）
　インピーダンスアナライザを用いて厚み共振周波数から電気機械結合定数を求める方法としては、電子情報技術産業協会規格ＪＥＩＴＡ　ＥＭ－４５０１（旧ＥＭＡＳ－６１００）圧電セラミック振動子の電気的試験方法に記載の円盤状振動子の厚みたて振動に４．２．６項に準拠している。上記評価結果を表１に示す。表１において、電気機械結合定数の保存後は試料を５０℃３５％ＲＨ環境下に３００時間放置後までのデータである。 k t = (α / tan ( α)) 1/2 However, α = (π / 2) × (S / P)
As a method of obtaining an electromechanical coupling constant from a thickness resonance frequency using an impedance analyzer, a disk-like vibration described in the electrical information testing method of the JEITA EM-4501 (formerly EMAS-6100) piezoelectric ceramic vibrator of the Japan Electronics and Information Technology Industries Association The thickness of the child is in compliance with paragraph 4.2.6. The evaluation results are shown in Table 1. In Table 1, after storage of the electromechanical coupling constant, the data is obtained after the sample was left in a 50 ° C. 35% RH environment for 300 hours.
　図１に本発明の試料１と比較の試料３の残留分極量のヒステリシス曲線を示す。また図２に電気機械結合定数の時間経過グラフを示す。 FIG. 1 shows hysteresis curves of remanent polarization amounts of the sample 1 of the present invention and the sample 3 for comparison. FIG. 2 shows a time course graph of the electromechanical coupling constant.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　表１に示した結果から明らかなように、本発明の範囲内で実施された試料については、圧電特性に優れており、残留モノマー量が少ない場合、分極後の保存により特性が劣化しにくいことが分かる。 As is apparent from the results shown in Table 1, the samples carried out within the scope of the present invention are excellent in piezoelectric characteristics, and when the residual monomer amount is small, the characteristics are not easily deteriorated by storage after polarization. I understand.
　実施例２
　（超音波探触子の作製と評価）
　（送信用圧電材料の作製）
　成分原料であるＣａＣＯ３、Ｌａ２Ｏ３、Ｂｉ２Ｏ３とＴｉＯ２、及び副成分原料であるＭｎＯを準備し、成分原料については、成分の最終組成が（Ｃａ０．９７Ｌａ０．０３）Ｂｉ４．０１Ｔｉ４Ｏ１５となるように秤量した。次に、純水を添加し、純水中でジルコニア製メディアを入れたボールミルにて８時間混合し、十分に乾燥を行い、混合粉体を得た。得られた混合粉体を、仮成形し、空気中、８００℃で２時間仮焼を行い仮焼物を作製した。次に、得られた仮焼物に純水を添加し、純水中でジルコニア製メディアを入れたボールミルにて微粉砕を行い、乾燥することにより圧電セラミックス原料粉末を作製した。微粉砕においては、微粉砕を行う時間および粉砕条件を変えることにより、それぞれ粒子径１００ｎｍの圧電セラミックス原料粉末を得た。それぞれ粒子径の異なる各圧電セラミックス原料粉末にバインダーとして純水を６質量％添加し、プレス成形して、厚み１００μｍの板状仮成形体とし、この板状仮成形体を真空パックした後、２３５ＭＰａの圧力でプレスにより成形した。次に、上記の成形体を焼成した。最終焼結体の厚さは２０μｍの焼結体を得た。なお、焼成温度は、それぞれ１１００℃であった。抗電界の１．５倍以上の電界を１分間印加して分極処理を施した。 Example 2
(Preparation and evaluation of ultrasonic probe)
(Production of piezoelectric material for transmission)
Component raw materials CaCO 3 , La 2 O 3 , Bi 2 O 3 and TiO 2 , and subcomponent raw materials MnO are prepared, and for the component raw materials, the final composition of the components is (Ca 0. 97 La 0.0 3 . ) Bi 4 . Weighed to be 01 Ti 4 O 15 . Next, pure water was added, mixed in a ball mill containing zirconia media in pure water for 8 hours, and sufficiently dried to obtain a mixed powder. The obtained mixed powder was temporarily molded and calcined in air at 800 ° C. for 2 hours to prepare a calcined product. Next, pure water was added to the obtained calcined material, finely pulverized in a ball mill containing zirconia media in pure water, and dried to prepare a piezoelectric ceramic raw material powder. In the fine pulverization, the piezoelectric ceramic raw material powder having a particle diameter of 100 nm was obtained by changing the pulverization time and pulverization conditions. 6% by mass of pure water as a binder is added to each piezoelectric ceramic raw material powder having a different particle diameter, press-molded to form a plate-shaped temporary molded body having a thickness of 100 μm, and this plate-shaped temporary molded body is vacuum-packed and then 235 MPa. It shape | molded by the press with the pressure of. Next, the molded body was fired. The final sintered body had a thickness of 20 μm. The firing temperature was 1100 ° C. Polarization treatment was performed by applying an electric field of 1.5 times or more of the coercive electric field for 1 minute.
　（受信用積層振動子の作製）
　前記実施例１において作製した電子線照射済みのポリフッ化ビニリデン共重合体のフィルム（有機圧電体膜）と厚さ５０μｍのポリエステルフィルムをエポキシ系接着剤にて貼り合わせた積層振動子を作製した。その後、上記と同様に分極処理をした。 (Production of laminated resonator for reception)
A laminated vibrator in which the electron beam irradiated polyvinylidene fluoride copolymer film (organic piezoelectric film) prepared in Example 1 and a 50 μm thick polyester film were bonded together with an epoxy adhesive was prepared. Thereafter, polarization treatment was performed in the same manner as described above.
　次に、常法に従って、上記の送信用圧電材料の上に受信用積層振動子を積層し、かつバッキング層と音響整合層を設置し超音波探触子を試作した。 Next, according to a conventional method, an ultrasonic probe was prototyped by laminating a laminated receiving transducer on the above-described piezoelectric material for transmission, and installing a backing layer and an acoustic matching layer.
　なお、比較例として、上記受信用積層振動子の代わりに、ポリフッ化ビニリデン共重合体のフィルム（有機圧電体膜）のみを用いた受信用積層振動子を上記受信用積層振動子に積層した以外、上記超音波探触子と同様の探触子を作製した。 As a comparative example, in place of the above laminated resonator for reception, a laminated resonator for reception using only a polyvinylidene fluoride copolymer film (organic piezoelectric film) was laminated on the above laminated resonator. A probe similar to the above-described ultrasonic probe was produced.
　次いで、上記２種の超音波探触子について受信感度と絶縁破壊強度の測定をして評価した。 Next, the above two types of ultrasonic probes were evaluated by measuring reception sensitivity and dielectric breakdown strength.
　なお、受信感度については、５ＭＨｚの基本周波数ｆ１を発信させ、受信２次高調波ｆ２として１０ＭＨｚ、３次高調波として１５ＭＨｚ、４次高調波として２０ＭＨｚの受信相対感度を求めた。受信相対感度は、ソノーラメディカルシステム社（Ｓｏｎｏｒａ　Ｍｅｄｉｃａｌ　Ｓｙｓｔｅｍ，Ｉｎｃ：２０２１Ｍｉｌｌｅｒ　Ｄｒｉｖｅ　Ｌｏｎｇｍｏｎｔ，Ｃｏｌｏｒａｄｏ（０５０１　ＵＳＡ））の音響強度測定システムＭｏｄｅｌ８０５（１～５０ＭＨｚ）を使用した。 Incidentally, the reception sensitivity is originating the fundamental frequency f 1 of 5 MHz, to determine the received relative sensitivity of 20MHz as 15 MHz, 4 harmonics as received second harmonic wave f 2 as 10 MHz, 3 harmonic. For the relative sensitivity of reception, a sound intensity measurement system Model 805 (1 to 50 MHz) of Sonora Medical System, Inc. (Sonora Medical System, Inc: 2021 Miller Drive Longmont, Colorado (0501 USA)) was used.
　絶縁破壊強度の測定は、負荷電力Ｐを５倍にして、１０時間試験した後、負荷電力を基準に戻して、相対受信感度を評価した。感度の低下が負荷試験前の１％以内のときを良、１％を超え１０％未満を可、１０％以上を不良として評価した。 The dielectric breakdown strength was measured by multiplying the load power P by 5 times, testing for 10 hours, and then returning the load power to the standard to evaluate the relative reception sensitivity. The sensitivity was evaluated as good when the decrease in sensitivity was within 1% before the load test, more than 1% and less than 10%, and 10% or more as bad.
　上記評価において、本発明に係る受信用圧電（体）積層振動子を具備した探触子は、比較例に対して約１．２倍の相対受信感度を有しており、かつ絶縁破壊強度は良好であることを確認した。すなわち、本発明の超音波振動子は、超音波医用画像診断装置に用いる超音波探触子にも好適に使用できることが確認された。 In the above evaluation, the probe including the receiving piezoelectric (body) laminated vibrator according to the present invention has a relative receiving sensitivity about 1.2 times that of the comparative example, and the dielectric breakdown strength is It was confirmed to be good. That is, it was confirmed that the ultrasonic transducer of the present invention can be suitably used for an ultrasonic probe used in an ultrasonic medical image diagnostic apparatus.

Claims (8)

  1. 超音波振動子を形成するための高分子量体からなる有機圧電材料であって、該有機圧電材料に含まれる、残モノマー量が２００ｐｐｍ以下であることを特徴とする有機圧電材料。 An organic piezoelectric material comprising a high molecular weight material for forming an ultrasonic vibrator, wherein the amount of residual monomer contained in the organic piezoelectric material is 200 ppm or less.
  2. 分極処理を経て形成される有機圧電材料であって、分極処理を施される前の前記有機圧電材料に含まれる、残モノマー量が２００ｐｐｍ以下であることを特徴とする請求の範囲第１項に記載の有機圧電材料。 The organic piezoelectric material formed through polarization treatment, wherein the amount of residual monomer contained in the organic piezoelectric material before being subjected to polarization treatment is 200 ppm or less. The organic piezoelectric material described.
  3. 有機圧電材料が延伸製膜工程を経て形成されていることを特徴とする請求の範囲第１項又は第２項に記載の有機圧電材料。 The organic piezoelectric material according to claim 1 or 2, wherein the organic piezoelectric material is formed through a stretching film forming step.
  4. 分極処理直後の有機圧電材料の電気機械結合定数が０．３～０．４であって、かつ前記分極処理直後の有機圧電材料を５０℃で環境下３００時間保存した後の電気機械結合定数が０．３～０．４であることを特徴とする請求の範囲第３項に記載の有機圧電材料。 The electromechanical coupling constant of the organic piezoelectric material immediately after the polarization treatment is 0.3 to 0.4, and the electromechanical coupling constant after storing the organic piezoelectric material immediately after the polarization treatment at 50 ° C. in an environment for 300 hours is 4. The organic piezoelectric material according to claim 3, wherein the organic piezoelectric material is 0.3 to 0.4.
  5. 前記有機圧電材料が、フッ化ビニリデンとトリフルオロエチレンの共重合体からなり、フッ化ビニリデンが９５～６０モル％、トリフルオロエチレン５～４０モル％の比率の範囲であることを特徴とする請求の範囲第１項～第４項のいずれか１項に記載の有機圧電材料。 The organic piezoelectric material is made of a copolymer of vinylidene fluoride and trifluoroethylene, and the ratio of vinylidene fluoride is 95 to 60 mol% and trifluoroethylene is 5 to 40 mol%. 5. The organic piezoelectric material according to any one of items 1 to 4 of the above range.
  6. 請求の範囲第１項～第５項のいずれか１項に記載の有機圧電材料の製造方法であって、該有機圧電材料の原料となる高分子量体を有機溶媒に溶解してフィルム状に形成する工程を有し、かつ前記原料となる高分子量体を有機溶媒の溶解前に減圧乾燥をすることを特徴とする有機圧電材料の製造方法。 The method for producing an organic piezoelectric material according to any one of claims 1 to 5, wherein a high molecular weight material that is a raw material of the organic piezoelectric material is dissolved in an organic solvent and formed into a film shape And a method for producing an organic piezoelectric material, comprising: drying the high molecular weight material as a raw material under reduced pressure before dissolving the organic solvent.
  7. 請求の範囲第１項～第５項のいずれか１項に記載の有機圧電材料を用いることを特徴とする超音波振動子。 An ultrasonic vibrator using the organic piezoelectric material according to any one of claims 1 to 5.
  8. 電気信号を発生する手段と、前記電気信号を受けて超音波を被検体に向けて送信し、前記被検体から受けた反射波に応じた受信信号を生成する複数の振動子が配置された超音波探触子と、前記超音波探触子が生成した前記受信信号に応じて、前記被検体の画像を生成する画像処理手段とを有する超音波医用画像診断装置において、前記超音波探触子が、送信用超音波振動子と受信用超音波振動子の両方を具備し、かつ、該超音波振動子のどちらか一方もしくは両方が請求の範囲第７項に記載の超音波振動子であることを特徴とする超音波医用画像診断装置。 Ultrasound in which a means for generating an electrical signal and a plurality of transducers for receiving the electrical signal and transmitting an ultrasonic wave toward the subject and generating a reception signal corresponding to the reflected wave received from the subject are arranged In the ultrasonic medical image diagnostic apparatus, comprising: an ultrasonic probe; and an image processing unit that generates an image of the subject according to the reception signal generated by the ultrasonic probe. Comprises both a transmitting ultrasonic transducer and a receiving ultrasonic transducer, and one or both of the ultrasonic transducers is the ultrasonic transducer according to claim 7. An ultrasonic medical image diagnostic apparatus characterized by the above.
PCT/JP2009/053372 2008-07-03 2009-02-25 Organic piezoelectric material, process for producing the organic piezoelectric material, ultrasonic vibrator, and ultrasonic image diagnosis apparatus for medical application WO2010001633A1 (en)

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