Filler for ultrasonic transducer and ultrasonic transducer using the same

Abstract

To provide a filler for an ultrasonic transducer that suppresses sub resonance and reverberation time, and an ultrasonic transducer using the same.SOLUTION: A filler for an ultrasonic transducer 1 of the present invention includes 100 pts. mass of resin, 20 to 150 pts. mass of inorganic filler, and 0.01 to 20 pts. mass of hollow material. By filling the filler for an ultrasonic transducer into a cylindrical case 5 provided with a piezoelectric material 3, sub resonance that occurs during transmission and reception of ultrasonic waves in the ultrasonic transducer is suppressed, and at the same time the reverberation time can be shortened.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a filler for an ultrasonic transducer and an ultrasonic transducer using the same. [Background technology]

[0002] Ultrasonic transducers are used as distance measuring sensors by transmitting and receiving ultrasonic waves to and from a test object using piezoelectric elements, etc., and measuring changes in the propagation time and frequency of the ultrasonic waves. They are widely used, for example, for functions such as automatic braking in automobiles and warning of nearby obstacles, and for detecting obstacles in mobile robots. In such ultrasonic transducers, from the viewpoint of improving the accuracy of short-distance detection, when ultrasonic waves reflected by a subject are received by a piezoelectric element, it is required to suppress, for example, sub-resonance and reverberation time within a housing in which the piezoelectric element is stored.

[0003] Patent Document 1 discloses a filler in which a foam made of silicone or polystyrene is mixed with a resin made of silicone or urethane, which is placed in a housing that houses a piezoelectric element. Patent Document 2 discloses a filler in which a foam body made of silicone or urethane is tightly attached to the center of the inner bottom surface of a housing. Patent Document 3 discloses a composition for damping vibration parts, which contains a resin and filler particles designed as hollow materials. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-118957 A [Patent Document 2] Patent Publication No. 2021-072589 [Patent Document 3] German Patent Publication No. 102012210513 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in Patent Document 1, the foam is crushed before use, which results in an irregular shape of the foam and an uneven distribution of the added foam in the molded product, making it difficult to control the properties. In Patent Document 2, since the foam is formed by gas generated by the material itself, it is difficult to control the cell shape, and as a result, it is difficult to keep the transducer characteristics due to the cell shape constant. Furthermore, since the generated gas escapes from the foam to the outside, it may form visible holes in the coating resin when heated, etc. Patent Document 3 describes the ratio of filler particles to be added and the range of particle size, but does not provide any examples relating to the improvement of ultrasonic vibration characteristics, nor does it describe or suggest the effectiveness of the filler particles.

[0006] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a filler for ultrasonic transducers that suppresses secondary resonance and reverberation time, and an ultrasonic transducer using the same. [Means for solving the problem]

[0007] As a result of extensive research to solve the above problems, the inventors discovered that by filling a filler material containing a resin, an inorganic filler, and a hollow material into a case equipped with a piezoelectric material, an ultrasonic transducer can be obtained in which secondary resonance and reverberation time during ultrasonic transmission and reception are suppressed, and thus completed the present invention.

[0008] That is, the present invention provides the following [1] to

[10] . [1] A filler for an ultrasonic transducer comprising: (A) a resin; (B) an inorganic filler; and (C) a hollow material. [2] The filler for ultrasonic transducers according to the above [1], comprising 20 to 150 parts by mass of the (B) inorganic filler and 0.01 to 20 parts by mass of the (C) hollow material, relative to 100 parts by mass of the (A) resin. [3] The filler for ultrasonic transducers according to the above [1] or [2], wherein the (A) resin is one or two selected from a silicone-based resin and a urethane-based resin. [4] The filler for ultrasonic transducers according to any one of the above [1] to [3], wherein the inorganic filler (B) has an average particle size of 0.5 μm to 10 μm. [5] The filler for ultrasonic transducers according to any one of the above [1] to [4], wherein the (B) inorganic filler is one or more selected from the group consisting of silica-based inorganic fillers, carbon black, alumina, titanium oxide, and graphite. [6] The filler for ultrasonic transducers according to any one of the above [1] to [5], wherein the hollow material (C) has an average particle size of 0.5 μm to 500 μm. [7] The filler for ultrasonic transducers according to any one of the above [1] to [6], wherein the true specific gravity of the hollow material (C) is 0.001 or more and less than 1.00. [8] The filler for ultrasonic transducers according to any one of the above [1] to [7], wherein the (C) hollow material is an organic hollow material. [9] The filler for ultrasonic transducers according to [8] above, wherein the organic hollow material is one or more selected from acrylonitrile-based resins, vinyl chloride-based resins, phenol-based resins, epoxy-based resins, and urea-based resins.

[10] An ultrasonic transducer using the filler for ultrasonic transducers according to any one of the above [1] to [9]. Effect of the Invention

[0009] According to the present invention, it is possible to provide a filler for an ultrasonic transducer that suppresses secondary resonance and reverberation time, and an ultrasonic transducer using the same. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a cross-sectional view showing an example of the configuration of an ultrasonic transducer used in an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] [Filling material for ultrasonic transducers] The filler for ultrasonic transducers of the present invention is characterized by containing (A) a resin, (B) an inorganic filler, and (C) a hollow material. In the present invention, by filling a case equipped with a piezoelectric material with a filling material including (A) a resin, (B) an inorganic filler, and (C) a hollow material, the secondary resonance that occurs when an ultrasonic transducer transmits and receives ultrasonic waves can be suppressed and at the same time the reverberation time can be shortened.

[0012] In this specification, preferred definitions may be selected arbitrarily, and combinations of preferred definitions may be considered more preferred. In this specification, the expression "XX to YY" means "at least XX and at most YY." In this specification, the lower limit and upper limit described in stages for the preferred numerical range (e.g., range of content, etc.) can be independently combined. For example, the description "preferably 10 to 90, more preferably 30 to 60" can be combined with the "preferable lower limit (10)" and the "more preferable upper limit (60)" to form "10 to 60."

[0013] [(A) Resin] The filler of the present invention contains a resin as an essential component. Examples of the resin include silicone resins, styrene resins, and urethane resins. The resins may be used alone or in combination of two or more. Among these, silicone resins and urethane resins are preferred, and silicone resins are more preferred.

[0014] Examples of silicone-based resins include curable silicone resins, silicone graft resins, and modified silicone resins such as alkyl-modified silicone resins, with reactive curable silicone resins being preferred. Examples of reactive curable silicone resins include addition reaction silicone resins, condensation reaction silicone resins, and ultraviolet or electron beam curable silicone resins. Of these, addition reaction type silicone resins are preferred because they have excellent weather resistance and are free from the risk of outgassing.

[0015] One embodiment of the addition reaction silicone resin is a resin obtained by curing a polydimethylsiloxane having vinyl groups introduced at the end or side chain with a hydrogensiloxane through a hydrosilylation reaction using a platinum catalyst.

[0016] As the addition reaction type silicone resin, commercially available products can be used, such as KE-109E A / B (manufactured by Shin-Etsu Chemical Co., Ltd.) and KE-106 A / B (manufactured by Shin-Etsu Chemical Co., Ltd.). In addition, examples of commercially available products of addition reaction type silicone resins (which contain a specified inorganic filler) include DOWSIL (registered trademark) 1817CV MA / B (manufactured by Dow-Toray Industries, Inc.) and DOWSIL (registered trademark) 1816CV MA / B (manufactured by Dow-Toray Industries, Inc.).

[0017] The silicone resin is cured by leaving it at room temperature for a certain period of time or by heating it for a certain period of time, depending on the silicone resin used. For example, the leaving time is 2 to 24 hours at room temperature, and the heating time is 30 minutes to 4 hours at 80 to 120°C.

[0018] [(B) Inorganic filler] The filler of the present invention contains an inorganic filler as an essential component. The inorganic filler is not particularly limited, but from the viewpoint of suppressing floating of hollow materials in the filling material and maintaining uniform dispersion, it is preferable to use one or more types selected from silica-based inorganic fillers, carbon black, alumina, titanium oxide, and graphite.

[0019] The inorganic filler preferably has an average particle size in the range of 0.5 to 10 μm, more preferably 1 to 8 μm, and further preferably 2 to 6 μm. An average particle size of 0.5 μm or more is preferable because it is possible to suppress thickening of the filler when the blending components are mixed. Moreover, it is preferable that the average particle size is 10 μm or less, since this allows the inorganic filler to be uniformly dispersed in the filling material. When the average particle size is within the above range, it becomes easier to impart a vibration-damping function to the filled molding. The average particle size can be determined by measurement using a microscope.

[0020] [(C) Hollow material] The filler of the present invention contains a hollow material as an essential component. The hollow material can uniformly reduce the density of the filled molding. The hollow material may be an inorganic hollow material or an organic hollow material as long as it can maintain the hollow particle shape in the filled molding. From the viewpoint of further reducing the density and impact resistance of the filled molding, it is preferable to use an organic hollow material. From the viewpoint of impact resistance, the organic hollow material is preferably one or more types selected from acrylonitrile-based resins, vinyl chloride-based resins, phenol-based resins, epoxy-based resins, and urea-based resins. In this specification, the hollow material is usually a hollow particle having a void in its hollow portion, and the outer shell component is a balloon made of the above-mentioned resin or the like, and the hollow portion is completely surrounded by the outer shell and does not penetrate to the outside via the outer shell.

[0021] The hollow material preferably has an average particle size in the range of 0.5 to 500 μm, more preferably 1 to 400 μm, even more preferably 10 to 300 μm, even more preferably 25 to 200 μm, and even more preferably 40 to 150 μm. By having an average particle size of 0.5 μm or more, the hollow material has a moderate surface area and good compatibility with resin, and the molded product obtained by using the filler can have sufficient mechanical strength. In addition, by having an average particle size of 500 μm or less, the hollow body is less likely to crack or collapse due to stress during mixing of the filler components, etc., which is preferable. Furthermore, if the average particle size is in the above-mentioned range, the density of the molded product can be reduced. The average particle size can be determined, for example, by measurement using a microscope.

[0022] From the viewpoints of reducing the density of the filled molding and maintaining the hollow particle shape of the hollow material, the true specific gravity of the hollow material is preferably 0.001 or more and less than 1.00, more preferably 0.005 to 0.90, even more preferably 0.01 to 0.80, and even more preferably 0.015 to 0.70. In this specification, the true specific gravity can be measured, for example, by a pycnometer method.

[0023] The filler of the present invention preferably contains 20 to 150 parts by mass of (B) inorganic filler and 0.01 to 20 parts by mass of (C) hollow material relative to 100 parts by mass of (A) resin, more preferably 40 to 130 parts by mass of (B) inorganic filler, 0.100 to 10 parts by mass of (C) hollow material, and even more preferably 60 to 110 parts by mass of (B) inorganic filler and 1.00 to 7 parts by mass of (C) hollow material. When the amount of the inorganic filler (B) and the hollow material (C) is within this range per 100 parts by mass of the resin (A), this tends to lead to suppression of secondary resonance of the ultrasonic transducer and shortening of the reverberation time.

[0024] [Other ingredients] The filler may contain optional components other than (A) the resin, (B) the inorganic filler, and (C) the hollow material, within the scope of not impairing the effects of the present invention. The total content of the filler other than the above-mentioned other components, i.e., (A) resin, (B) inorganic filler, and (C) hollow material, is preferably 50 to 99 mass%, more preferably 60 to 98 mass%, and even more preferably 70 to 97 mass%.

[0025] Examples of other components include a curing agent, a silane coupling agent, a colorant, a dispersant, etc. These may be used alone or in combination of two or more.

[0026] For example, when the resin is a urethane resin, an isocyanate compound can be used as the curing agent. The isocyanate compound is a compound having two or more isocyanate groups in the molecule. Examples of the isocyanate compound include tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), and naphthalene diisocyanate (NDI).

[0027] Examples of the silane coupling agent include vinyl-based silane compounds, epoxy-based silane compounds, styryl-based silane compounds, methacryl-based silane compounds, acrylic-based silane compounds, amino-based silane compounds, and mercapto-based silane compounds.

[0028] As the colorant, for example, inorganic pigments such as titanium dioxide or iron oxide, organic pigments such as phthalocyanine blue, and various dyes can be used. The inorganic pigment can also be (B) inorganic filler, and may be the material described in the above section (B) inorganic filler. One or more of these may be selected. The amount of colorant added may be appropriately determined according to the desired color tone, etc.

[0029] The dispersant is not particularly limited, and examples thereof include low molecular weight dispersants such as fatty acid salts (soaps) and alkyl sulfates, and polymeric dispersants such as polyacrylates and polyvinyl alcohol.

[0030] The filler of the present invention is for use in ultrasonic transducers, and can be suitably used in particular in ultrasonic transducers used in ultrasonic sensors or ultrasonic sonars for measuring distances in space or underwater.

[0031] 1 is a cross-sectional view showing an example of the configuration of an ultrasonic transducer used in an embodiment of the present invention, in which ultrasonic transducer 1 has a piezoelectric material 3 on the inner bottom of a cylindrical case 5, and a filler 2 is filled in cylindrical case 5. A pair of signal electrodes 4 facing each other so as to sandwich the piezoelectric material 3 therebetween are electrically connected to pin terminals 7 by lead wires 6.

[0032] (Piezoelectric material) The piezoelectric material has the function of transmitting and receiving ultrasonic waves. The center frequency of the ultrasonic waves generated by the piezoelectric material can be appropriately selected depending on the object to be examined, but is usually 20 kHz or more when the human audible range is taken into consideration. For example, when used for vehicle-mounted applications for obstacle detection, the center frequency is preferably 40 kHz to 90 kHz, and can be appropriately selected depending on the application. The thickness of the piezoelectric material in the ultrasonic wave propagation direction is not particularly limited, but can be appropriately selected depending on the type of ultrasonic transducer and the oscillation frequency, and is usually 100 μm to 300 μm.

[0033] Examples of piezoelectric materials include piezoelectric ceramics such as lead zirconate titanate (PZT)-based piezoelectric ceramics; piezoelectric single crystals such as lead magnesium niobate-lead titanate solid solution (PMN-PT) and lead zinc niobate-lead titanate solid solution (PZN-PT); and non-lead piezoelectric materials include potassium sodium niobate (KNN)-based compounds represented by the general formula (K,Na)NbO3. Furthermore, composite piezoelectric materials that combine these materials with polymeric materials are also included. Examples of polymeric materials include polyvinylidene fluoride (PVDF), vinylidene fluoride-trifluoroethylene copolymer (P(VDF / TrFE)), vinylidene cyanide-vinyl acetate copolymer (P(VDCN / VAc)), etc.

[0034] Signal electrodes are disposed on both sides of the piezoelectric material. When a voltage is applied to the signal electrode, the piezoelectric material bends upward or downward. Therefore, when a voltage that fluctuates like a sine wave is applied to the signal electrode, the piezoelectric material vibrates up and down. This causes the pressure on the surrounding air to fluctuate, changing the density of the air and transmitting ultrasound. In contrast, if the voltage of the signal electrode can be measured without applying a voltage to the signal electrode (keeping the impedance high), the piezoelectric material will deform when it receives ultrasound reflected from the subject, causing a change in voltage. The waveform of this voltage can be acquired via the signal electrode and analyzed to detect the ultrasound. The signal electrode is electrically connected to the piezoelectric material via the pin terminal and lead wire described above, and as long as signals can be transmitted between the signal electrode and the piezoelectric material, there are no particular restrictions on the material. For example, a layer made of gold, nickel, molybdenum, silver, aluminum, palladium, platinum, copper, or an alloy thereof can be used.

[0035] An ultrasonic transducer basically has a piezoelectric material for transmitting and receiving ultrasonic waves, but taking into consideration performance, placement space, etc., the piezoelectric material for transmitting ultrasonic waves and the piezoelectric material for receiving ultrasonic waves may be arranged separately or stacked.

[0036] [Manufacturing method of filler for ultrasonic transducers] The method for producing the filler for ultrasonic transducers of the present invention is not particularly limited, and the filler can be obtained by blending and mixing the above-mentioned blending components of the filler. The order of addition of the compounding components when compounding them is not particularly limited, and each compounding component may be compounded and mixed at the same time. It is also preferable to add hollow materials that may crack or be crushed during mixing later, taking into consideration the load that they will receive from mixing. The mixing of the blended components can be carried out using a known stirrer or mixer, such as stirring with a rotor blade or a planetary stirrer mixer. From the viewpoint of suppressing outgassing and bubble entrapment, it is preferable to perform degassing under reduced pressure during mixing. The filler of the present invention is excellent in degassing under reduced pressure.

[0037] When the above-mentioned filler for ultrasonic transducers is produced, it is preferable to produce it by the following method. First, the resin, inorganic filler, and hollow material are blended and mixed, and then the mixing is continued under reduced pressure to degas the mixture, thereby obtaining a filler. According to such a manufacturing method, it is possible to preferably obtain a filler for ultrasonic transducers in which bubble entrapment is suppressed, the hollow material does not float, and the inorganic filler and hollow material can be uniformly dispersed and retained in the filler. The reduced pressure during defoaming may be a degree of vacuum that can be achieved by a general reduced pressure defoamer.

[0038] [Filler molded product] The method for producing a filled molding using a filler is not particularly limited, but it is preferable to produce the filled molding by, for example, casting the filler in a predetermined mold, heating it, and curing it. The heating temperature is appropriately set according to the curing temperature of the resin used. When a filler molding is cut out from a hardened filler and molded, the hollow material is prone to cracking or crushing. Therefore, it is preferable to mold the filler molding by pouring it into a mold that has been prepared in advance to match the shape and size of the desired filler molding.

[0039] For example, when an ultrasonic transducer equipped with a filler molding has a function such as warning of nearby obstacles, the reverberation time is preferably 5 ms or less, more preferably 3 ms or less, and even more preferably 2 ms or less. It is also preferable that secondary resonance does not occur. EXAMPLES

[0040] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto.

[0041] [Filler ingredients] Details of the blending components of each filler produced in the Examples and Comparative Examples are as follows. <(A) Resin> Silicone resin: Resin components of both liquid A and liquid B of DOWSIL (registered trademark) 1817CV MA / B (manufactured by Dow Toray) (common) <(B) Inorganic filler> Silica particles and carbon particles: Inorganic filler component of "DOWSIL (registered trademark) 1817CV MA (Dow Toray)" (mixture of silica particles and carbon particles: irregular shape; average particle size 4.42 μm) Silica particles: inorganic filler component of "DOWSIL (registered trademark) 1817CV MB (Dow Toray)" (silica particles: irregular; average particle size: 6.28 μm) Here, the average particle size of the inorganic filler was calculated as follows. First, the inorganic filler component was separated from the above-mentioned solution A by the separation described below to obtain a mixture of silica particles and carbon particles. Also, the inorganic filler component was separated from the above-mentioned solution B to obtain silica particles. Next, the separated inorganic filler was photographed using a scanning electron microscope (S-4800, manufactured by Hitachi High-Technologies Corporation) at an acceleration voltage of 5 kV and a magnification of ×500. The photographed image was binarized using image processing software (LUZEX AP, manufactured by Nireco Corporation), and the particle diameter r of each inorganic filler contained in the image was taken as the area S of each particle, giving a circle equivalent diameter r=(4 / π×S). 1 / 2 The arithmetic mean of the particle diameters r of each particle thus determined was taken as the average particle diameter contained in liquid A and liquid B. <(C) Hollow material> Resin balloon: Matsumoto Microsphere F80-DE, manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd., spherical shape; average particle size 90-130 μm, shell composition acrylonitrile copolymer, solid content 97% by mass or more, true specific gravity 0.020 ± 0.005 <Ingredients used in Comparative Examples 4 and 5> Epoxy resin: jER828, manufactured by Mitsubishi Chemical Corporation (Bisphenol A type, specific gravity 1.17) (Hardening agent: 2E4MZ, manufactured by Shikoku Kasei Co., Ltd.) Inorganic filler: Mn-Zn ferrite: MZ05S, Powdertech Co., Ltd. (D10: 1.5 μm, D50: 2.7 μm, D90: 5.9 μm, Dmax: 13.6 μm; D10, D50, and D90 are, in this order, the particle sizes at 10%, 50%, and 90% cumulative from the small diameter side in a volume-based particle size distribution obtained, for example, by a laser diffraction method.) Solid body: Silicone rubber powder: KMP-605, manufactured by Shin-Etsu Chemical Co., Ltd. (True specific gravity 0.99, average particle size 2μm)

[0042] The resin component and the inorganic filler component were obtained by separating liquids A and B of "DOWSIL (registered trademark) 1817CV MA / B (manufactured by Dow-Toray Industries, Inc.)" using a high-speed refrigerated centrifuge (manufactured by Hitachi Koki Co., Ltd., model name: CR20GII) at a rotation speed of 5000 rpm for 30 minutes.

[0043] Example 1 [Preparation of hardened filler] 3.18 parts by mass of resin balloons were added as hollow materials to the A and B liquids (100 parts by mass of silicone resin, 91.4 parts by mass of inorganic filler (86.1 parts by mass of silica particles, 5.3 parts by mass of carbon particles)) of "DOWSIL (registered trademark) 1817CV MA / B (manufactured by Dow Toray Co., Ltd.)" and mixed for 3 minutes using a planetary stirring mixer (manufactured by Kurabo Industries, Ltd., model name: KK-V350W). Next, the target vacuum pressure by the vacuum pump was set to 0.0 Pa, and mixing under reduced pressure was continued for 2.5 minutes to degas the material, thereby obtaining a filler. Next, the obtained filler was potted on an Al flat plate, and 3 mm thick spacers were placed on each of the four outer periphery sides of the Al flat plate, and the material was sandwiched between other Al flat plates of the same size, and then heated (100°C, 1 hour) to produce a hardened filler.

[0044] [Preparation of ultrasonic transducer] The ultrasonic transducer for evaluation shown in FIG. 1 was fabricated in the following manner. First, a piezoelectric material 3 made of PZT was bonded to the inner bottom surface of a bottomed cylindrical case 5. The piezoelectric material 3 used had pin terminals 7 and lead wires 6. Next, the bottomed cylindrical case 5 was filled with transducer filler 2, which was then heated and cured to produce an ultrasonic transducer.

[0045] Comparative Example 1 A cured product of the filler and an ultrasonic transducer were produced in the same manner as in Example 1, except that no hollow material was added.

[0046] Comparative Example 2 A cured filler and an ultrasonic transducer were produced in the same manner as in Example 1, except that the silicone resin separated by the above-mentioned separation in Example 1 was not added.

[0047] Comparative Example 3 A cured filler and an ultrasonic transducer were produced in the same manner as in Example 1, except that only the silicone resin separated by the above-mentioned separation was used.

[0048] Comparative Example 4 [Preparation of hardened filler] 100 parts by mass of epoxy resin (Mitsubishi Chemical Corporation, jER828), 3 parts by mass of hardener (Shikoku Kasei Co., Ltd., 2E4MZ), 53.5 parts by mass of inorganic filler (Powder Tech Co., Ltd., Mn-Zn ferrite, MZ05S), 5.13 parts by mass of silicone rubber powder (Shin-Etsu Chemical Co., Ltd., KMP-605) were added, and mixed for 3 minutes using a planetary stirring mixer (Kurabo Industries, Ltd., model name: KK-V350W). Next, the target vacuum pressure by the vacuum pump was set to 0.0 Pa, and mixing under reduced pressure was continued for 2 and a half minutes to degas the mixture, thereby obtaining a filler. Next, the obtained filler was potted on an Al plate, and 3 mm thick spacers were placed on each of the four outer periphery sides of the Al plate, and the mixture was sandwiched between other Al plates of the same size, and then heated (100°C, 1 hour) to produce a cured product of the filler.

[0049] [Preparation of ultrasonic transducer] In the same manner as in Example 1, an ultrasonic transducer for evaluation shown in FIG.

[0050] Comparative Example 5 A cured filler and an ultrasonic transducer were produced in the same manner as in Comparative Example 4, except that the silicone resin separated by the above-mentioned separation was used instead of the epoxy resin (jER828) in Comparative Example 4.

[0051] [Measurement evaluation] The cured products of the fillers obtained in the above Examples and Comparative Examples were subjected to the following various measurements and evaluations. The evaluation results are summarized in Table 1 below.

[0052] (Shore A hardness) The cured fillers obtained in the examples and comparative examples were prepared as two-ply test pieces (20 mm long x 45 mm wide x 3 mm thick). The Shore A hardness was measured using a rubber hardness tester Type A (manufactured by Kobunshi Keiki Co., Ltd., model name: JA) in accordance with JIS K 6253-3: Vulcanized rubber and thermoplastic rubber - Determination of hardness. The results are shown in Table 1.

[0053] (Storage modulus, loss modulus, and loss factor) The cured fillers obtained in the examples and comparative examples (excluding comparative examples 4 and 5) were used as test pieces (diameter 9 mm x thickness 3 mm) to measure the storage modulus (25°C) and loss modulus (25°C) using a dynamic viscoelasticity measuring device (NETZSCH; model name: DMA242E, compression mode, temperature range: -40 to 130°C, heating rate: 2°C / min, measurement frequency: 1 Hz, strain: 0.25%). The loss factor (tan δ) was calculated from the ratio of the loss modulus to the storage modulus. The results are shown in Table 1.

[0054] (Appearance evaluation of molded products) The appearance of the cured products of the fillers produced in the Examples and Comparative Examples was evaluated according to the following criteria. 〇: Uniform with no resin segregation ×: Resin segregation on the bottom surface The results are shown in Table 1.

[0055] (Reverberation time) Using the ultrasonic transducers produced in the examples and comparative examples, the intensity was adjusted so that the transmitted sound pressure of the ultrasonic sensor was 100 dB while checking with an oscilloscope. Then, 20 pulse waves were transmitted, and the attenuation of the transmitted sound pressure was observed with an oscilloscope. The time when the 20th pulse wave was transmitted (sound pressure 100 dB) was set to 0, and the time until the sound pressure became 64 dB or less was set as the reverberation time (ms) (25°C). In the present invention, the reverberation time was evaluated according to the following criteria. ○: Reverberation time is 2.0 ms or less ×: Reverberation time exceeds 2.0 ms The measurement results (reverberation time only) are shown in Table 1.

[0056] (sub-resonance) The ultrasonic transducers produced in the examples and comparative examples were connected to an impedance analyzer (HIOKI, IM3570), and the conductance value (G value) was measured while sweeping the frequency in the range of 40 kHz to 90 kHz with an applied voltage of 0.5 V, and a graph (FG graph) showing the relationship between frequency and conductance value was output. The minimum G value was subtracted from the output FG graph to correct the G value in the corrected FG graph, and the peak with the maximum peak top was determined as the main resonance, and the corrected FG graph was divided by the G value (Gmax) of the main resonance. In the intensity ratio FG graph thus obtained, the peaks with an intensity ratio of 0.1 or more other than the main resonance peak were determined as the secondary resonance (25°C). The secondary resonance was evaluated according to the following criteria. 〇: No secondary resonance ×: There is secondary resonance The results are shown in Table 1.

[0057] [Table 1]

[0058] From the results shown in Table 1, it can be seen that the ultrasonic transducer of Example 1 of the present invention, which is constructed using a filler containing (A) resin, (B) inorganic filler, and (C) hollow material, has a shorter reverberation time and suppresses secondary resonance, compared to the ultrasonic transducer of Comparative Example 1, which is constructed using a filler containing (A) resin and (B) inorganic filler, the ultrasonic transducer of Comparative Example 2, which is constructed using a filler containing (A) resin and (C) hollow material, and the ultrasonic transducer of Comparative Example 3, which is constructed using a filler containing only (A) resin. Similarly, the ultrasonic transducer of Example 1 of the present invention, which is constructed using a filler including (A) resin, (B) inorganic filler, and (C) hollow material, has a shorter reverberation time and suppresses secondary resonances, as compared with the ultrasonic transducer of Comparative Example 4, which is constructed using an epoxy resin as the (A) resin, Mn-Zn ferrite as the filler corresponding to the (B) inorganic filler, and a filler including a solid material (silicone rubber powder) instead of the (C) hollow material, and the ultrasonic transducer of Comparative Example 5, which is constructed using the same (A) resin, Mn-Zn ferrite as the filler corresponding to the (B) inorganic filler, and a filler including a solid material (silicone rubber powder) instead of the (C) hollow material. [Industrial Applicability]

[0059] Since the filler for ultrasonic transducers suppresses secondary resonance and reverberation time, and an ultrasonic transducer using the same is used, it is conceivable that the filler can be used in functions such as automatic braking in automobiles and warnings of nearby obstacles, and in ultrasonic sensors used for obstacle detection in mobile robots. [Explanation of symbols]

[0060] 1: Ultrasonic transducer 2: Filler molded product 3: Piezoelectric material 4: Signal electrode 5: Cylindrical case 6: Lead wire 7: Pin terminal

Claims

1. A filler for an ultrasonic transducer comprising: (A) a resin; (B) an inorganic filler; and (C) a hollow material.

2. 2. The ultrasonic transducer filler according to claim 1, comprising 20 to 150 parts by mass of the inorganic filler (B) and 0.01 to 20 parts by mass of the hollow material (C) relative to 100 parts by mass of the resin (A).

3. 3. The filler for ultrasonic transducers according to claim 1, wherein the resin (A) is one or two selected from the group consisting of silicone-based resins and urethane-based resins.

4. 3. The filler for ultrasonic transducers according to claim 1, wherein the inorganic filler (B) has an average particle size of 0.5 μm to 10 μm.

5. 3. The filler for ultrasonic transducers according to claim 1, wherein the inorganic filler (B) is one or more selected from the group consisting of silica-based inorganic fillers, carbon black, alumina, titanium oxide, and graphite.

6. 3. The filler for ultrasonic transducers according to claim 1, wherein the hollow material (C) has an average particle size of 0.5 μm to 500 μm.

7. 3. The filler for ultrasonic transducers according to claim 1 or 2, wherein the hollow material (C) has a true specific gravity of 0.001 or more and less than 1.

00.

8. 3. The filler for ultrasonic transducers according to claim 1, wherein the hollow material (C) is an organic hollow material.

9. 9. The filler for ultrasonic transducers according to claim 8, wherein the organic hollow material is one or more selected from the group consisting of acrylonitrile-based resins, vinyl chloride-based resins, phenol-based resins, epoxy-based resins, and urea-based resins.

10. 3. An ultrasonic transducer comprising the filler for ultrasonic transducers according to claim 1 or 2.

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