Resin composition

Abstract

To produce a resin composition that features low attenuation and applicability for coating.SOLUTION: A resin composition according to an embodiment is a resin composition that is a precursor of an acoustic matching layer for an ultrasound transducer in an ultrasound transducer unit having an array transducer including a piezoelectric body and an electrode, and the resin composition includes a resin and particles of an inorganic material, and satisfies 2.3≤Z / √ρ≤3.4 where Z denotes an acoustic impedance of the acoustic matching layer and ρ denotes a density of the particles of the inorganic material.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The embodiments disclosed in this specification and the drawings relate to a resin composition.

Background Art

[0002] In an ultrasonic diagnostic apparatus, it is required to thin piezoelectric elements and acoustic matching layers. In addition, the element size of an array oscillator is required to be miniaturized in accordance with the higher frequency of transmitted and received ultrasonic waves.

[0003] Here, conventionally, an acoustic matching layer has been created by laminating a glass plate, a carbon plate, or the like with an adhesive. However, as the acoustic matching substrate of the acoustic matching layer has been thinned, it has become difficult to handle the substrate and laminate it with an adhesive. In addition, the technical difficulty of processing the substrate of the acoustic matching layer has also increased.

[0004] Therefore, for example, as shown in Patent Document 1, a method of adjusting acoustic impedance by mixing a high-density ceramic or metal filler in which nanoparticles and microparticles are mixed in a resin, and laminating the acoustic matching layer by applying the mixture to the acoustic matching layer is conceivable.

[0005] However, this method is limited to the case where the density of ceramic particles is high, and since it is a method of mixing particles of different sizes, there is a problem in maintaining the in-plane uniformity of the impedance of the thin-film acoustic matching layer.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to produce a resin composition with low attenuation and capable of being coated. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problems. The problems corresponding to the respective effects of each configuration shown in the embodiments described later can also be positioned as other problems.

Means for Solving the Problems

[0008] The resin composition according to the embodiment is a resin composition that is a precursor of an acoustic matching layer of an ultrasonic vibrator in an ultrasonic vibrator unit having an array vibrator including a piezoelectric body and an electrode. The resin composition contains a resin and inorganic material particles. When the acoustic impedance of the acoustic matching layer is Z and the density of the inorganic material particles is ρ, 2.3 ≦ Z / √ρ ≦ 3.4 is satisfied.

Brief Description of the Drawings

[0009]

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DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the resin composition will be described in detail with reference to the drawings.

[0011] (First Embodiment) First, with reference to FIG. 1, an example of the configuration of an ultrasonic diagnostic apparatus incorporating an ultrasonic vibrator generated using the resin composition according to the embodiment will be described.

[0012] As shown in FIG. 1, the ultrasonic diagnostic apparatus 100 includes an ultrasonic probe 1, a monitor 2, an input device 3, and a device main body 10.

[0013] The ultrasonic probe 1 has an ultrasonic vibrator unit that transmits ultrasonic waves and receives reflected waves

[0014] FIG. 2 shows a partial configuration of the ultrasonic vibrator unit.

[0015] The ultrasonic oscillator unit is built into the ultrasonic probe 1 and transmits and receives ultrasonic waves to and from the living body that the probe contacts. The ultrasonic oscillator unit is composed of, for example, a plurality of ultrasonic oscillators 23 arranged two-dimensionally, a flexible printed circuit (FPC) 22 on which the plurality of ultrasonic oscillators 23 are arranged, and an acoustic lens. Each of the plurality of ultrasonic oscillators 23 is composed of a piezoelectric element 21, an acoustic matching layer 20, and a back matching layer (not shown). The element size 24 of the ultrasonic oscillator 23 is, for example, 40 μm.

[0016] The piezoelectric element 21 is an element having piezoelectricity. For example, the piezoelectric element 21 is a piezoelectric element such as PZT (lead zirconate titanate / Pb(Zr,Ti)O3), PMN-PT (lead magnesium niobate-lead titanate / Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3). In the embodiment, the plurality of ultrasonic oscillators 23 are arranged and provided on a predetermined surface of the flexible printed circuit board 22. A signal electrode is provided on the surface of the piezoelectric element 21 on the side from which ultrasonic waves are radiated (the ultrasonic radiation surface). Also, a ground electrode is provided on the surface (the back surface) of the piezoelectric element 21 opposite to the ultrasonic radiation surface side.

[0017] The piezoelectric element 21 is driven by a drive signal from the transmission / reception circuit 11 to radiate ultrasonic waves from the surface on the signal electrode side. Also, when the piezoelectric element 21 receives a reflected wave, it converts the received reflected wave into a reflected wave signal and outputs the converted reflected wave signal from the signal electrode. The thickness of the piezoelectric element 21 is, for example, 40 μm.

[0018] The acoustic matching layer 20 is a layer for gradually reducing the acoustic impedance from the piezoelectric element 21 to the living body and acoustically matching the piezoelectric element 21 with the living body. The acoustic matching layer 20 may be composed of only one layer, or may have a plurality of layers in order to reduce the acoustic impedance as smoothly as possible toward the living body. As the acoustic matching layer 20, for example, a resin mixed with a conductive filler can be used to impart conductivity. This resin can be, for example, an epoxy resin. The thickness of the acoustic matching layer 20 is, for example, 30 μm.

[0019] In addition, the back surface matching layer is made of a material having a higher acoustic impedance than the piezoelectric element, and serves as a resonance layer to transmit and receive ultrasonic waves integrally with the piezoelectric element.

[0020] Also, the flexible printed circuit board 22 is an FPC (Flexible Printed Circuit), and electrically connects the signal electrode and the ground electrode to the transmission and reception circuit 11 via the wirings provided in each layer of the ultrasonic vibrator.

[0021] In addition, between the piezoelectric element 21 and the acoustic matching layer 20, for example, an adhesive may be filled, or it may be generated by lamination coating without using an adhesive.

[0022] When ultrasonic waves are transmitted from the ultrasonic probe 1 to the subject P, the transmitted ultrasonic waves are successively reflected at the discontinuous surfaces of the acoustic impedance in the body tissues of the subject P, and are received by a plurality of ultrasonic vibrators 23 of the ultrasonic probe 1 as reflected waves. The reflected wave is converted into a reflected wave signal, which is an electrical signal, by the piezoelectric element 21 of the ultrasonic vibrator 23 that received the reflected wave. The amplitude of the reflected wave signal depends on the difference in acoustic impedance at the discontinuous surface where the ultrasonic wave is reflected. Note that when the transmitted ultrasonic pulse is reflected from the surface of a moving blood flow, heart wall, etc., the reflected wave signal undergoes a frequency shift depending on the velocity component of the moving object with respect to the ultrasonic transmission direction due to the Doppler effect.

[0023] The monitor 2 displays a GUI (Graphical User Interface) for an operator of the ultrasonic diagnostic apparatus 100 to input various setting requests using the input device 3, or displays ultrasonic images and the like generated in the apparatus main body 10.

[0024] The input device 3 has a trackball, switches, dials, a touch command screen, and the like. The input device 3 receives various setting requests from an operator of the ultrasonic diagnostic apparatus 100 and transfers the received various setting requests to the apparatus main body 10.

[0025] The apparatus main body 10 is a device that controls transmission and reception of ultrasonic waves by the ultrasonic probe 1 and generates an ultrasonic image based on the reflected waves received by the ultrasonic probe 1. As shown in FIG. 1, the apparatus main body 10 includes a transmission / reception circuit 11, a B-mode processing circuit 12, a Doppler processing circuit 13, a processing circuit 14, and a memory 15.

[0026] The transmission / reception circuit 11 includes a trigger generation circuit, a delay circuit, a pulsar circuit, and the like, and supplies a drive signal to the ultrasonic probe 1.

[0027] The B-mode processing circuit 12 receives reflected wave data from the transmission / reception circuit 11, performs logarithmic amplification, envelope detection processing, and the like, and generates data (B-mode data) in which the signal intensity is represented by the brightness of the luminance.

[0028] The Doppler processing circuit 13 frequency-analyzes velocity information from the reflected wave data received from the transmission / reception circuit 11, extracts blood flow, tissue, and contrast agent echo components due to the Doppler effect, and generates data (Doppler data) in which moving body information such as average velocity, variance, and power is extracted for multiple points.

[0029] The processing circuit 14 is configured by a control processor (CPU: Central Processing Unit) that realizes functions as, for example, an information processing device (computer).

[0030] The processing circuit 14 generates an ultrasonic image from the data generated by the B-mode processing circuit 12 and the Doppler processing circuit 13 by means of an image generation function. Further, the processing circuit 14 controls the processing of the transmission / reception circuit 11, the B-mode processing circuit 12, the Doppler processing circuit 13, etc. based on various setting requests input from the operator via the input device 3 and various control programs and various data read from the memory 15 by means of a control function.

[0031] The memory 15 is a memory that stores the ultrasonic image generated by the processing circuit 14 by means of the image generation function 14a. Further, the memory 15 can also store the data generated by the B-mode processing circuit 12 or the Doppler processing circuit 13.

[0032] Subsequently, the background according to the embodiment will be described. In the ultrasonic diagnostic apparatus 100, for the purpose of improving the resolution of the acquired image or for the purpose of obtaining information on a three-dimensional space, etc., the array vibrator tends to be required to be composed of a larger number of ultrasonic vibrators 23. On the other hand, the ultrasonic probe 1 is required to transmit and receive ultrasonic waves at a higher frequency (shorter wavelength). For this reason, the piezoelectric element 21, the acoustic matching layer 20, etc. tend to be required to be thinned.

[0033] Also, it is desirable that the element size 24 of the ultrasonic vibrator 23 be miniaturized in accordance with the higher frequency of the transmitted and received ultrasonic waves.

[0034] Here, conventionally, the acoustic matching layer 20 has been generated by laminating a glass plate, a carbon plate, etc. with an adhesive, but as the acoustic matching base material of the acoustic matching layer 20 has been thinned, it has become difficult to handle the base material and laminate it with an adhesive. In addition, the technical difficulty of processing the base material of the acoustic matching layer 20 has also increased.

[0035] Therefore, as shown in Patent Document 1, a process has been proposed in which the acoustic impedance Z is adjusted by mixing a high-density ceramic or a metal filler in which particles of nanometer size and particles of micrometer size are mixed in a resin, and the mixture is applied to the acoustic matching layer 20 to laminate the acoustic matching layer 20.

[0036] However, the method of Patent Document 1 is a method limited to the case where the density ρ of the ceramic particles is high, and since it is a method of mixing particles of different sizes, there are problems in terms of the in-plane uniformity of the impedance of the thin film acoustic matching layer.

[0037] The resin composition according to the embodiment is based on such a background. The resin composition according to the embodiment is a resin composition that is a precursor of the acoustic matching layer 20 of the ultrasonic oscillator 24 in an ultrasonic oscillator unit having an array oscillator including a piezoelectric body composed of the piezoelectric element 21 and an electrode. The resin composition contains a resin and inorganic material particles, and when the acoustic impedance of the acoustic matching layer 20 is Z and the density of the ceramic particles is ρ, it satisfies 2.3 ≤ Z / √ρ ≤ 3.4. Here, in the first embodiment, the inorganic material particles are ceramic particles. That is, in the first embodiment, the resin composition contains a resin and ceramic particles, and when the acoustic impedance of the acoustic matching layer 20 is Z and the density of the ceramic particles is ρ, it satisfies 2.3 ≤ Z / √ρ ≤ 3.4.

[0038] Here, regarding the quantity Z / √ρ, generally, when the acoustic impedance is Z and the density of the substance is ρ, Z / √ρ is a quantity related to the bulk modulus. That is, Z / √ρ is generally a quantity representing the difficulty of deformation of the substance. However, in the embodiment, for the resin composition composed of a resin and ceramic particles, the value of Z / √ρ is evaluated with respect to the density ρ of the added ceramic particles, not the density of the resin composition itself.

[0039] Here, the relationship between the value of Z / √ρ and the properties of the resin composition will be described with reference to FIG. 3. FIG. 3 is a graph showing the design value of the acoustic impedance Z on the horizontal axis and the density ρ of the ceramic particles added to the resin on the vertical axis, and explaining the properties of the resin composition.

[0040] Here, in FIG. 3, curves 50, 51, and 52 are curves where Z / √ρ = 2.3, 2.85, and 3.4 respectively, and the region between curve 50 and curve 52, for example, the region 41 shown as region B, becomes the optimal composition as the resin composition. On the other hand, the low-viscosity region 42 on the left side of curve 50 shown as region A and the high-viscosity region 43 on the right side of curve 52 shown as region C are regions that are not suitable as the resin composition.

[0041] More specifically, in the low-viscosity region 42, the density of the added ceramic particles is high, and it becomes a region where sedimentation of the high-density ceramic particles occurs. Also, in the low-viscosity region 42, the density of the ceramic particles is high, there is a lot of reflection scattering, and strong attenuation occurs. That is, the low-viscosity region 42 is a region that is not suitable as the resin composition due to sedimentation of the ceramic particles and attenuation in reflection scattering.

[0042] On the other hand, in the high-viscosity region 43, since a high-viscosity and highly thixotropic paste is formed, mixing, degassing, and spreading / coating become technically difficult. As an example, in the high-viscosity region 43, in the process of forming a uniform thin film (<100 μm) by coating with a slit coat or an applicator, sufficient coating accuracy cannot be obtained, and manufacturing problems occur. That is, the high-viscosity region 43 is a region that is not suitable as the resin composition due to manufacturing problems.

[0043] Therefore, regarding the first advantage of the resin composition according to the embodiment, by satisfying 2.3 ≦ Z / √ρ ≦ 3.4, it becomes a low-attenuation and coatable one, and becomes an appropriate resin composition.

[0044] That is, the resin composition according to the embodiment becomes low-attenuation in the design range of the appropriate acoustic impedance Z of 3.0 to 15 MRayl. Also, the resin composition according to the embodiment has a viscosity that can be coated in the range of 1 < Cp < 500 [Pas] at the shear viscosity at the coating shear rate by, for example, a slit coat or an applicator.

[0045] Next, regarding the second advantage of the resin composition according to the embodiment, the resin composition according to the embodiment uses ceramic particles with a unimodal particle size to produce the resin composition, rather than mixing particles of different sizes.

[0046] Briefly explaining this point, regarding the particle size of the ceramic particles added to the resin, in order to ensure the in-plane uniformity of the impedance of the thin film acoustic matching layer, it is required to have a small particle size. Here, for example, when mixing particles with two peak particle sizes of large and small as in Patent Document 1 and Patent Document 2, the viscosity adjustment becomes easy, but it becomes difficult to avoid mixing large particle size fillers. As a result, in places where there are many large particle size fillers, the acoustic impedance Z will vary in the thickness direction. In addition, as shown in FIG. 4, when large particle size fillers dispersed in the acoustic matching layer 20 slide down 32 or remain 31 during the dicing process when configuring the ultrasonic vibrator 23, it will cause variations in the acoustic impedance Z between the ultrasonic vibrators 23. In particular, in the ultrasonic vibrator 23 where the transmitted ultrasonic wave has a higher frequency, since the element size 24 of the ultrasonic vibrator 23 is miniaturized, the variations between the elements of the ultrasonic vibrator 23 become prominent. Therefore, it is desirable that the particle size distribution of the average particle size of the ceramic particles according to the embodiment is a unimodal distribution. When adding ceramic particles with a unimodal particle size to produce the resin composition, the in-plane uniformity of the impedance Z of the acoustic matching layer 20 is improved, and the variations in the acoustic impedance Z between the array vibrators are reduced.

[0047] The resin composition according to the embodiment contains a resin such as an epoxy resin and ceramic particles, and is a material in a form that does not contain fine bubbles or the like that cause attenuation and in which the ceramic particles are uniformly dispersed. The uniformly dispersed state can be realized by the stirring method described later.

[0048] [Regarding Ceramic Particles] As the ceramic particles added to the resin composition according to the embodiment, ceramic particles generally used as small particle size fillers can be widely used. As an example, the ceramic particles contain a substance composed of at least one of Mg, Ca, Ba, B, Al, Y, Hf, Ce, Ti, W, and Si and at least one of O, C, N, and S. The average particle size (average primary particle size) of the ceramic particles is typically in the small particle size range of 0.3 μm or more and 2.0 μm or less from the viewpoint of suppressing the variation in the viscosity of the acoustic matching layer composition and the acoustic impedance between the array vibrators as described above. As an example, the ceramic particles may contain 5% by volume or less of particles having a particle size of 2.0 μm or less or 0.005 μm or more. The ceramic particle material and each content are appropriately adjusted within the range of 2.3 ≦ Z / √ρ ≦ 3.4 with respect to the designed acoustic impedance Z.

[0049] [Regarding the resin] Examples of the resin constituting the resin composition according to the embodiment include epoxy resins. More specifically, ordinary epoxy resins such as aliphatic cyclic (alicyclic) epoxy resins, bisphenol A type epoxy resins, bisphenol F type epoxy resins, and phenol novolac type epoxy resins can be mentioned. In the embodiment, in order to coat the filler dispersion composition, it is preferable to use a low-viscosity epoxy resin. The viscosity of the epoxy resin is desirably 500 mPas or less at 24°C.

[0050] The epoxy resin used in the embodiment is not particularly limited, and epoxy resins generally used as the main component of epoxy adhesives can be widely used. As a specific example, for example, Celoxide 2021P (registered trademark), which is an aliphatic cyclic (alicyclic) epoxy resin, can be mentioned. Compared with general-purpose epi-bis type epoxy resins, it is characterized by being a low-viscosity liquid with an extremely low chlorine content and has the advantage of being easy to operate in the coating process.

[0051] Note that the epoxy resin may consist of the above epoxy resin, or may contain other epoxy resins within a range that does not impair the effects of the present embodiment in addition to the above epoxy resin. The epoxy resin may be used alone or in combination of two or more.

[0052] As the curing agent, those known as curing agents for epoxy resins can be used without particular limitation. For example, a thermosetting resin can be used as a curing agent for the epoxy resin. Examples of typical curing agents include, for example, tertiary amines, imidazoles, Lewis acids, Bronsted bases, acid anhydrides, aliphatic amines, aromatic amines, dicyandiamide, dihydrazide compounds, phenolic resins, and the like. As curing agents that can avoid affecting the viscosity of the epoxy resin and maintain the low viscosity of the main agent, catalytic tertiary amines, imidazoles, Lewis acids, and Bronsted bases are easy to operate. Specific examples include borate-based cationic polymerizers, SI series manufactured by Sun-Aid (registered trademark), etc.

[0053] [Regarding the mixing ratio of resin and ceramic particles] The epoxy content in the layer material of the embodiment is preferably 60 to 80% by mass. Also, the ceramic content in the layer material of the embodiment is preferably 20 to 40% by mass. That is, typically, the content of ceramic particles in the resin composition is 20% by volume or more and 40% by volume or less.

[0054] [Regarding the mixing process of resin and ceramic particles] Points to note regarding the mixing process of the resin and ceramic particles include the following three points. That is, first, that each component can be uniformly mixed, second, that the mixed air can be properly degassed, and third, that mixing is performed under low-temperature conditions that can suppress the start of the heat-curing reaction. As the mixing method, for example, it is preferable to knead using a planetary mixer with a vacuum degassing mechanism. However, heat is generated by the friction between the fillers at this time. An example of the flow of the mixing process will be described in detail in the following examples.

[0055] [Regarding the Coating Process and Curing] The coating process of the acoustic matching layer composition according to the embodiment will be described. The acoustic matching layer composition purified by the above-described method is coatable, and examples of specific coating methods include slit coating and coating with an applicator. Taking coating with an applicator as an example, the thickness of the matching layer can be controlled by the gap of the applicator and the coating speed.

[0056] Note that the configuration of the matching layer is not limited to a single layer. For example, after finishing the coating of the first layer, by changing the gap of the applicator, the second layer of the matching layer can be coated on the first layer of the coated matching layer, and the third layer of the matching layer can be coated on the second layer of the coated matching layer, and so on. With such a configuration, it is possible to laminate and coat an acoustic matching layer composition having a plurality of acoustic impedances without using an adhesive. Further, the coated matching layer can be heat-cured in a clean oven to obtain a sheet-like single-layer or multi-layer acoustic matching sheet.

[0057] [Regarding Curing] Curing shrinkage that occurs when the resin matching layer cures and linear expansion that occurs in the heating process are the causes of warping of the resin matching layer. Therefore, as the cured resin, it is recommended to use a room temperature curing resin or a UV curing resin. However, when a room temperature curing resin is used as in Patent Document 1, the temperature may rise due to contact and frictional heat between the fillers in the mixing process of the resin and the filler, and the polymerization reaction may start and cure. Further, when a photocuring resin is used as in Patent Document 2, curing unevenness may occur in the depth direction because the filler absorbs and scatters light.

[0058] On the other hand, the above-described coating process is a high-precision coating process that does not induce warping of the resin acoustic matching layer even when a heat-curing resin (cured at 150 ° C) is used.

[0059] The above is a description of the outline of the resin composition according to the embodiment. Hereinafter, specific examples of the resin composition according to the embodiment will be described. In the first example of the first embodiment, the case of adding aluminum oxide (Al2O3) is considered when creating the ultrasonic probe 1 with a center frequency of 20 - 30 MHz. In the second embodiment, the case of adding tungsten carbide (WC) is described considering the case of creating the ultrasonic probe 1 with a center frequency of about 30 MHz.

[0060] (The first example of the first embodiment) In the first example of the first embodiment, the case of using aluminum oxide (Al2O3) as the ceramic particles added to the resin is described assuming the case of creating the ultrasonic probe 1 with a center frequency of 20 - 30 MHz.

[0061] [Regarding the selection of ceramic particles] First, the reason for selecting aluminum oxide (Al2O3) as the ceramic particles added to the resin when creating the ultrasonic probe 1 with a center frequency of 20 - 30 MHz will be explained.

[0062] As factors related to the acoustic matching layer, the designed value of the acoustic impedance was set to Z = 5.6 [MRayl], the designed value of the film thickness of the acoustic matching layer 20 was set to 30 μm, and the designed value of the element size 24 was set to 40 μm.

[0063] Also, as a constraint condition, the attenuation coefficient of the acoustic matching layer composition generated by the reflection and scattering of the filler was set to less than 0.6 dB / MHz / mm at a center frequency of 20 - 30 MHz. Under the above - mentioned designed values and constraint conditions, the possible compositions of ceramic particles were examined.

[0064] Here, based on the relational expression 2.3 ≤ Z / √ρ ≤ 3.4 between the acoustic impedance Z and the density ρ of the ceramic particles as the filler to be added, the composition calculation was performed at Z / √ρ = 2.85, which is the intermediate value of these relational expressions. Substituting Z = 5.6 [MRayl], which is the designed value of the acoustic impedance, we get ρ = [3.99 g·cm^3]. In the first embodiment of the first example, considering various conditions such as being a group of commonly used ceramic materials as the small particle-based filler having a density close to this value, aluminum oxide (Al2O3: ρ = [3.8 g·cm^3]) was selected.

[0065] [Regarding the particle size of the ceramic particles] Next, considering the particle size of the ceramic particles as the filler to be added, if there are defects with a size of 5% or more with respect to the matching layer film thickness or the element size in the upper limit value of the particle size, it will directly affect the variation in the acoustic characteristics of each array element. Therefore, it is desirable that the upper limit value of the particle size does not exceed 5% of the matching layer film thickness or the element size. Considering that the designed value of the matching layer film thickness is 30 μm and the designed value of the element size is 40 μm, the particle size of the ceramic particles as the filler to be added is desirably 1.5 μm or less.

[0066] Based on the above considerations, in the first embodiment of the first example, commercially available Al2O3 with an average particle size of 0.7 μm (ρ = [3.8 g·cm^3]) was selected as the ceramic particles to be added in the first embodiment.

[0067] [Regarding the case where the designed value of the acoustic impedance Z is changed] Substituting the density of the filler ρ = [3.8 g·cm^3] into the relational expression 2.3 ≤ Z / √ρ ≤ 3.4 between the acoustic impedance Z and the density ρ of the ceramic particles as the filler to be added, we get 4.48 < Z < 6.63 [MRayl]. Therefore, the acoustic impedance Z can be changed within this range. Fig. 5 shows the experimental results of examining the properties of the generated acoustic matching layer composition by changing the value of the acoustic impedance Z in the range of Z = 4.1 to 8.

[0068] Here, for example, at Z = 4.1 [MRayl] corresponding to the low-viscosity region 42 shown as region A in FIG. 3, sedimentation of the filler occurred, and a thin film layer composed only of epoxy was formed on the outermost surface without uniform dispersion of the filler, so that it could not be used as an acoustic matching layer composition. Further, at Z = 7.2 to 8.0 [MRayl] corresponding to the high-viscosity region 43 shown as region C in FIG. 3, due to the high viscosity, precise coating with a designed film thickness t = 30 μm (coating error <+ / -1 μm) was impossible with slit coating or applicator coating methods. Note that since samples for acoustic impedance measurement use substrates with thicknesses of 1 mm, 2 mm, and 3 mm, formation and measurement are possible even with a material having a certain degree of high viscosity. In the region of Z = 4.6 to 6.3, such problems did not occur.

[0069] [Regarding the resin] Next, the resin to be mixed with the ceramic particles will be described. As the resin to be mixed with the ceramic particles, for example, an epoxy resin can be considered. In the first example of the first embodiment, as the epoxy resin to be mixed with the ceramic particles, for example, Celoxide 2021P (registered trademark) of Daicel Corporation (registered trademark) was selected. This material is a liquid epoxy resin with a low viscosity (250 mPas @ 24°C) and is suitable for an acoustic matching layer composition for coating purposes.

[0070] [Regarding the mixing ratio of the resin and the ceramic particles] Subsequently, the mixing amount of the resin and the ceramic particles will be described. By appropriately adjusting the mixing ratio of the resin and the ceramic particles, the value of the acoustic impedance Z can be adjusted. Substituting the density ρ = [3.8 g·cm^3] of Al2O3 into the relational expression 2.3 ≦ Z / √ρ ≦ 3.4 between the acoustic impedance Z and the density ρ of the ceramic particles as the filler to be added, 4.48 < Z < 6.63 [MRayl] is obtained. Therefore, the value of the acoustic impedance Z can be adjusted by changing the mixing amount of the resin and the ceramic particles. In the example, when the addition of the ceramic particles as the filler in epoxy + hardener + filler was 30 vol% by volume ratio, the acoustic impedance Z of the obtained resin composition was Z = 5.6 [MRayl].

[0071] [Regarding the curing agent] Next, the curing agent will be described. As the curing agent, a borate-based cationic polymerizing agent can be considered. In the examples, SI-B3A (registered trademark) manufactured by Sun-Aid (registered trademark) was added at 0.15 vol%. Note that since it is difficult to uniformly disperse the addition of the solid curing agent in the resin. For example, it is conceivable to dilute the curing agent with MEK (methyl ethyl ketone), add it so that the addition amount of the curing agent becomes 0.15 vol%, and remove MEK by vacuum degassing.

[0072] [Regarding the mixing process of the resin and ceramic particles] Subsequently, the mixing process of the resin, the ceramic particles as the filler, and the curing agent will be described. FIG. 6 shows an example of such a mixing flow. As for the mixing of the resin, the ceramic particles, and the curing agent, for example, it is conceivable to perform the mixing using a planetary stirrer with a vacuum degassing mechanism.

[0073] Specifically, first, 18.6 g of Celoxide 2021P (registered trademark) of Daicel Corporation (registered trademark) was weighed as the epoxy resin (first step). Subsequently, 25.5 g of Al2O3 filler was weighed (second step). Subsequently, the Al2O3 filler, which is the ceramic particles weighed in the second step, and Celoxide 2021P (registered trademark) weighed in the first step were uniformly dispersed at 2000 rpm for 2 minutes (third step). Subsequently, after confirming the uniform dispersion, the fine bubbles mixed in by stirring at 2000 rpm for 4 minutes were removed by evacuation to 0.2 Pa (fourth step). Subsequently, the mixed solution of the Al2O3 filler and Celoxide 2021P heated by the high-speed rotation treatment was cooled to 25 ° C (room temperature) (fifth step). Subsequently, the planetary stirrer heated by the high-speed rotation treatment was cooled to 25 ° C (room temperature) (sixth step).

[0074] Subsequently, 0.15 vol% of the curing agent: SI-B3A was dissolved in MEK and added to the composition obtained in the sixth step (seventh step). Subsequently, 0.005 vol% of Stabilizer with respect to Celoxide 2021P (registered trademark) was dissolved in ethanol and added (eighth step). Note that the eighth step can be omitted. Subsequently, in order to suppress the temperature rise of the mixed solution during rotation, it was stirred in a vacuum at a low rotation speed (500 rpm) for 1 minute to defoam the residual solvent and fine bubbles (ninth step). Subsequently, it was stirred in a vacuum at 200 rpm for 8 minutes (tenth step). Subsequently, after visually confirming that there was no defoaming from the surface of the mixed solution (eleventh step), the mixed composition was transferred to a dispensing syringe (twelfth step). Subsequently, the mixed solution of the Al2O3 filler and Celoxide 2021P (registered trademark) heated by high-speed rotation treatment was cooled to 25°C (thirteenth step). Subsequently, the planetary mixer heated by high-speed rotation treatment was cooled to 25°C (room temperature) with a cooling jig (fourteenth step). Subsequently, the bubbles remaining in the syringe were stirred in a vacuum at 200 rpm for 4 minutes (fifteenth step).

[0075] Through the above steps, it becomes possible to mix the Al2O3 filler and Celoxide 2021P (registered trademark) after adding the curing agent at 35°C or lower. Under the above mixing conditions, it became possible to control the pot life (viscosity change rate 2 hours after adding the curing agent) of the acoustic matching layer composition with Z = 5.6 [MRayl] to less than 5%.

[0076] In the slit coating or applicator coating process, the viscosity change of the composition directly affects the coating film thickness, so it is not desirable from the viewpoint of film thickness controllability. When a matching layer with a designed matching layer film thickness of 30 μm was formed by coating, it was confirmed that the coating film thickness fluctuation amount could be controlled to less than +0.1 μm with a viscosity increase rate of less than 5% in the current process.

[0077] (Second Example of the First Embodiment) In the second example of the first embodiment, the case of using tungsten carbide (WC) as the ceramic particles added to the resin will be described assuming the case of creating the ultrasonic probe 1 with a center frequency of 30 MHz.

[0078] [Regarding the Selection of Ceramic Particles] First, when fabricating the ultrasonic probe 1 with a center frequency of 30 MHz, the reason for selecting tungsten carbide (WC) as the ceramic particles to be added to the resin will be explained.

[0079] Regarding the factors related to the acoustic matching layer, the design value of the acoustic impedance was set to Z = 11 [MRayl], which is close to that of the glass matching layer, the design value of the matching layer film thickness was set to 40 μm, and the design value of the element size was set to 40 μm.

[0080] Also, as a constraint condition, the attenuation coefficient of the acoustic matching layer composition generated by the reflection and scattering of the filler was set to less than 0.6 dB / MHz / mm under the center frequency of 20 - 30 MHz. Under the above design values and constraint conditions, the composition of the ceramic particles that can be realized was investigated.

[0081] Here, based on the relational expression 2.3 ≦ Z / √ρ ≦ 3.4 between the acoustic impedance Z and the density ρ of the ceramic particles as the filler to be added, the composition calculation was performed at Z / √ρ = 2.85, which is the intermediate value of these relational expressions. Substituting the design value of the acoustic impedance Z = 11 [MRayl], ρ = [14.9 g·cm^3] is obtained. In the second example of the first embodiment, considering various conditions such as being a small particle-based filler having a density close to this value and being a group of commonly used ceramic materials, WC (ρ = [15.63 g·cm^3]) was selected.

[0082] [Regarding the Particle Size of Ceramic Particles] Next, considering the particle size of the ceramic particles which are the filler to be added, the upper limit value of the particle size of the particles should not exceed 5% of the thickness of the matching layer or the element size, because if there are defects with a size of 5% or more with respect to the thickness of the matching layer or the element size, it will directly affect the variation in the acoustic characteristics of each array element. Therefore, considering that the designed value of the thickness of the matching layer is 30 μm and the designed value of the element size is 40 μm, the particle size of the ceramic particles which are the filler to be added is desirably 1.5 μm or less.

[0083] Based on the above considerations, in the second example of the first embodiment, WC with an average particle size of 1.5 μm (a commercially available material with ρ = [15.63 g·cm^3]) was selected as the ceramic particles to be added in the second example of the first embodiment.

[0084] [Regarding the resin] Next, the resin to be mixed with the ceramic particles will be described. As the resin to be mixed with the ceramic particles, for example, an epoxy resin can be considered. In the second example of the first embodiment, similar to the first example of the first embodiment, as the epoxy resin to be mixed with the ceramic particles, for example, Celoxide 2021P (registered trademark) of Daicel Corporation (registered trademark) was selected. This material is a liquid epoxy resin with a low viscosity (250 mPas @ 24°C) and is suitable for the acoustic matching layer composition for coating purposes.

[0085] [Regarding the mixing ratio of the resin and the ceramic particles] Next, the mixing amount of the resin and the ceramic particles will be described. By appropriately adjusting the mixing ratio of the resin and the ceramic particles, the value of the acoustic impedance Z can be adjusted. Substituting the density ρ = [15.63 g·cm^3] of WC into the relational expression 2.3 ≦ Z / √ρ ≦ 3.4 between the acoustic impedance Z and the density ρ of the ceramic particles as the filler to be added, 9.1 < Z < 13.8 [MRayl] is obtained. Therefore, by changing the mixing amount of the resin and the ceramic particles, the value of the acoustic impedance Z can be adjusted. In the example, when the addition of the ceramic particles as the filler in epoxy + hardener + filler was 30 vol% in terms of volume ratio, the acoustic impedance Z of the obtained resin composition was Z = 11.0 [MRayl].

[0086] [Regarding the hardener] Next, the hardener will be described. As the hardener, it is conceivable to use a borate-based cationic polymerizing agent. In the example, SI-B3A (registered trademark) manufactured by Sun-Aid (registered trademark) was added at 0.15 vol%. Note that since it is difficult to uniformly disperse the addition of the hardener in the solid state in the resin. For example, it is conceivable to dilute the hardener with MEK (methyl ethyl ketone), add it so that the addition amount of the hardener becomes 0.15 vol%, and remove MEK by vacuum degassing.

[0087] [Regarding the mixing process of the resin and the ceramic particles] Subsequently, the mixing process of the resin, the ceramic particles as the filler, and the hardener will be described. By going through the same mixing process as that of the first example of the first embodiment shown in FIG. 6, the resin, the ceramic particles as the filler, and the hardener can be mixed. That is, for example, by using a rotating and revolving stirrer with a vacuum degassing mechanism for mixing, the resin, the ceramic particles as the filler, and the hardener can be mixed. The volume ratio of the ceramic particles to be mixed is about 30% as in the first example of the first embodiment. However, in the second embodiment, since WC, which is the ceramic particle to be mixed, has a high density, the weight to be mixed increases as compared with FIG. 6.

[0088] Through the above process, it becomes possible to mix the WC filler and Celloxide 2021P (registered trademark) at 35°C or lower. Under the above mixing conditions, it has become possible to control the pot life (viscosity change rate 2 hours after adding the curing agent) of the acoustic matching layer composition with Z = 11.0 [MRayl] to less than 5%.

[0089] In the slit coating and applicator coating processes, the viscosity change of the composition directly affects the coating film thickness, so it is not desirable from the viewpoint of film thickness controllability. When a matching layer with a designed matching layer film thickness of 30 μm was formed by coating, it was confirmed that the coating film thickness fluctuation amount could be controlled to less than +0.1 μm with a viscosity increase rate of less than 5% in the current process.

[0090] According to at least one embodiment described above, a resin composition with low attenuation and capable of being applied can be produced.

[0091] (Second Embodiment) In the first embodiment, the case where the particles of the inorganic material are ceramic particles was described. In the second embodiment, the case where the particles of the inorganic material are metal particles will be described.

[0092] FIG. 7 shows an example of a partial configuration of the ultrasonic oscillator unit 1070 according to the second embodiment.

[0093] The ultrasonic oscillator unit 1070 is built into the ultrasonic probe 1 and transmits and receives ultrasonic waves to and from the living body with which the probe contacts. The ultrasonic oscillator unit 1070 is composed of, for example, a plurality of ultrasonic oscillators arranged two-dimensionally, a flexible printed circuit (FPC) 1022 on which the plurality of ultrasonic oscillators are arranged, and an acoustic lens. Each of the plurality of ultrasonic oscillators is composed of a piezoelectric element 1021, an acoustic matching layer 1020, and a back matching layer (not shown). The element size 1027 of the ultrasonic oscillator is, for example, 40 μm.

[0094] The piezoelectric element 1021 is an element having piezoelectricity. For example, the piezoelectric element 1021 is a piezoelectric element such as PZT (lead zirconate titanate / Pb(Zr,Ti)O3), PMN-PT (lead magnesium niobate-lead titanate / Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3). In an embodiment, a plurality of ultrasonic transducers are arranged and provided on a predetermined surface of the flexible wiring board 1022. A signal electrode is provided on the surface (ultrasonic radiation surface) of the piezoelectric element 1021 from which ultrasonic waves are radiated. Also, a ground electrode is provided on the surface (back surface) of the piezoelectric element 1021 opposite to the ultrasonic radiation surface side.

[0095] The piezoelectric element 1021 is driven by a drive signal from the transmission / reception circuit 1011 to radiate ultrasonic waves from the surface on the signal electrode side. Also, when the piezoelectric element 1021 receives a reflected wave, it converts the received reflected wave into a reflected wave signal and outputs the converted reflected wave signal from the signal electrode. The thickness of the piezoelectric element 1021 is, for example, 40 μm.

[0096] The acoustic matching layer 1020 is a layer for gradually reducing the acoustic impedance from the piezoelectric element 1021 to the living body and acoustically matching the piezoelectric element 1021 and the living body. The acoustic matching layer 1020 may be composed of only one layer, or may have a plurality of layers in order to reduce the acoustic impedance as smoothly as possible toward the living body. As the acoustic matching layer 1020, for example, a resin mixed with a conductive filler can be used to impart conductivity. This resin can be, for example, an epoxy resin. The thickness of the acoustic matching layer 1020 is, for example, 30 μm.

[0097] Also, the back surface matching layer is made of a material having a higher acoustic impedance than the piezoelectric element, and serves as a resonance layer to transmit and receive ultrasonic waves integrally with the piezoelectric element.

[0098] Further, the flexible printed circuit board 1022 is an FPC (Flexible Printed Circuit), and electrically connects the signal electrode and the ground electrode to the transmission and reception circuit 11 via the wiring provided in each layer of the ultrasonic vibrator.

[0099] Further, between the piezoelectric element 1021 and the acoustic matching layer 1020, for example, an adhesive may be filled, or it may be formed by lamination coating without using an adhesive.

[0100] Subsequently, the background related to the second embodiment will be described. In the ultrasonic diagnostic apparatus 100, for the purpose of improving the resolution of the acquired image or obtaining information on a three-dimensional space, etc., the array vibrator tends to be required to be composed of a larger number of ultrasonic vibrators. On the other hand, the ultrasonic probe 1 is required to transmit and receive ultrasonic waves at a higher frequency (shorter wavelength). For this reason, the piezoelectric element 1021, the acoustic matching layer 1020, etc. tend to be required to be thinned.

[0101] Also, the element size of the ultrasonic vibrator is desirably miniaturized in accordance with the higher frequency of the transmitted and received ultrasonic waves.

[0102] Here, conventionally, the acoustic matching layer 1020 has been generated by laminating a glass plate, a carbon plate, etc. with an adhesive, but as the acoustic matching base material of the acoustic matching layer 1020 becomes thinner, it has become difficult to handle the base material and laminate it with an adhesive. In addition, the technical difficulty of processing the base material of the acoustic matching layer 1020 has also increased.

[0103] Therefore, as shown in Patent Document 1, a process has been proposed in which the acoustic impedance Z is adjusted by mixing a high-density ceramic or the like in which nanoparticles and microparticles are mixed in a resin, and the mixture is applied to the acoustic matching layer 1020 to laminate the acoustic matching layer 1020.

[0104] However, the method of Patent Document 1 is limited to the case where the density ρ of the ceramic particles is high, and since it is a method of mixing particles of different sizes, there are problems in terms of the in-plane uniformity of the impedance of the thin-film acoustic matching layer.

[0105] The resin composition according to the second embodiment is based on such a background and is based on the method of adding metal particles. The resin composition according to the embodiment is a resin composition that is a precursor of the acoustic matching layer 1020 of the ultrasonic oscillator 1024 in an ultrasonic oscillator unit having an array oscillator including a piezoelectric body composed of the piezoelectric element 1021 and an electrode. The resin composition contains a resin and metal particles, and when the acoustic impedance of the acoustic matching layer 1020 is Z and the density of the metal particles is ρ, it satisfies 2.3 ≤ Z / √ρ ≤ 2.9.

[0106] Here, regarding the quantity Z / √ρ, generally, when the acoustic impedance is Z and the density of the substance is ρ, Z / √ρ is a quantity related to the bulk modulus. That is, Z / √ρ is generally a quantity representing the difficulty of deformation of the substance. However, in the embodiment, for the resin composition composed of a resin and metal particles, the value of Z / √ρ is evaluated with respect to the density ρ of the added metal particles, rather than the density of the resin composition itself.

[0107] Here, the relationship between the value of Z / √ρ and the properties of the resin composition will be described with reference to FIG. 8. FIG. 8 is a graph showing the acoustic impedance Z on the horizontal axis and the density ρ of the metal particles added to the resin on the vertical axis, and explaining the properties of the resin composition.

[0108] Here, in FIG. 8, the straight lines 1050 and 1052 are straight lines with values of Z / √ρ = 2.3 and 2.9 that respectively represent the lower and upper limits of the aforementioned inequality 2.3 ≦ Z / √ρ ≦ 2.9, and the straight line 1051 is a straight line where the value of ρ is intermediate between the values of the straight lines 1050 and 1052. Regions between the straight lines 1050 and 1052, such as regions 1060a, 1060b, 1060c, 1060d, etc., are the optimal compositions as resin compositions. On the other hand, the low-viscosity region 1042 on the left side of the straight line 1050 and the high-viscosity region 1043 on the right side of the straight line 1052 are regions that are not suitable as resin compositions.

[0109] More specifically, in the low-viscosity region 1042, the density of the added metal particles is high, and it becomes a region where sedimentation of the high-density metal particles occurs. Also, in the low-viscosity region 1042, due to the influence of the average inter-particle distance, a problem of strong attenuation due to reflection scattering occurs. That is, the low-viscosity region 1042 is not a suitable region as a resin composition due to sedimentation of metal particles and attenuation in reflection scattering.

[0110] On the other hand, in the high-viscosity region 1043, since a high-viscosity and highly thixotropic paste is formed, mixing, degassing, and spreading / coating become technically difficult. As an example, in the high-viscosity region 1043, in the process of forming a uniform thin film (<100 μm) in coating by a slit coat or an applicator, sufficient coating accuracy cannot be obtained, and manufacturing problems occur. That is, the high-viscosity region 1043 is not a suitable region as a resin composition due to manufacturing problems.

[0111] Therefore, regarding the first advantage of the resin composition according to the embodiment, when explaining, the metal particle material according to the embodiment satisfies 2.3 ≦ Z / √ρ ≦ 2.9 in the relationship between the density ρ of the metal particle material and the designed acoustic impedance Z, resulting in a low-attenuation and coatable material, which becomes an appropriate resin composition.

[0112] That is, the resin composition according to the embodiment has low attenuation within the design range of the appropriate acoustic impedance Z of 3.0 to 15 MRayl. Further, the resin composition according to the embodiment has a viscosity such that it can be applied within the range of 1 < Cp < 500 [Pas] for the shear viscosity at the coating shear rate by, for example, slit coating or an applicator.

[0113] Next, regarding the second advantage of the resin composition according to the embodiment, the resin composition according to the embodiment is produced using mainly metal particles with a unimodal particle size of a small particle size, rather than mixing particles of different sizes.

[0114] Briefly explaining this point, regarding the particle size of the metal particles added to the resin, in order to ensure the in-plane uniformity of the impedance of the thin film acoustic matching layer, it is required to be of a small particle size. Here, for example, when mixing particles with a bimodal particle size of large and small as in Patent Document 1 and Patent Document 2, the viscosity adjustment becomes easy, but it becomes difficult to avoid mixing large particle size fillers. As a result, in portions where there are many large particle size fillers, the acoustic impedance Z varies in the thickness direction. In addition, if large particle size fillers dispersed in the acoustic matching layer 1020 slip or remain during the dicing process when forming the ultrasonic vibrator, it causes variations in the acoustic impedance Z between the ultrasonic vibrators. In particular, in ultrasonic vibrators where the transmitted ultrasonic waves have a higher frequency, since the element size is miniaturized, the variations between the elements of the ultrasonic vibrator become significant. Therefore, it is desirable that the particle size distribution of the average particle diameter of the metal particles according to the embodiment is a unimodal distribution of a small particle size. When adding metal particles with a unimodal particle size to produce the resin composition, the in-plane uniformity of the impedance Z of the acoustic matching layer 1020 is improved, and the variations in the acoustic impedance Z between the array vibrators are reduced. That is, it is possible to reduce the variations in the acoustic impedance between the array vibrators, and it is also possible to provide a resin composition with low attenuation and capable of being applied.

[0115] In addition, in the embodiment, it is possible to use a single material and find a material with an appropriate density available at an appropriate powder particle size. That is, when the resin and metal particles are mixed at an appropriate volume ratio, the viscosity and the formation of a thixotropic paste to form the composition make the coating very easy, and manufacturing problems are solved. Also, it is possible to control the reflection scattering attenuation generated by the addition of the filler to low attenuation.

[0116] Further, the resin composition according to the embodiment contains a resin such as an epoxy resin and metal particles, and is a material in a form that does not contain fine bubbles or the like that cause attenuation and in which the metal particles are uniformly dispersed. The uniformly dispersed state can be realized by the stirring method described later.

[0117] [Regarding the resin] Here, examples of the resin constituting the resin composition according to the embodiment include epoxy resins. More specifically, ordinary epoxy resins such as aliphatic cyclic (alicyclic) epoxy resins, bisphenol A type epoxy resins, bisphenol F type epoxy resins, and phenol novolak type epoxy resins can be mentioned. In the embodiment, in order to coat the filler dispersion composition, it is preferable to use a low-viscosity epoxy resin. The viscosity of the epoxy resin is desirably 500 mPas or less at 24°C.

[0118] The epoxy resin used in the embodiment is not particularly limited, and epoxy resins generally used as the main component of epoxy adhesives can be widely used. As a specific example, for instance, Celoxide 2021P (registered trademark), which is an aliphatic cyclic (alicyclic) epoxy resin, can be mentioned. Compared with general-purpose epi-bis type epoxy resins, it is characterized by being a low-viscosity liquid with an extremely low chlorine content, and has the advantage of being easy to operate in the coating process.

[0119] Note that the epoxy resin may be composed of the above epoxy resin, or in addition to the above epoxy resin, other epoxy resins may be contained within a range that does not impair the effects of the present embodiment. The epoxy resin may be used alone or in combination of two or more kinds.

[0120] [Regarding the curing agent] As the curing agent, those known as curing agents for epoxy resins can be used without particular limitation. For example, a thermosetting resin can be used as a curing agent for the epoxy resin. Examples of typical curing agents include, for example, tertiary amines, imidazoles, Lewis acids, Bronsted bases, acid anhydrides, aliphatic amines, aromatic amines, dicyandiamide, dihydrazide compounds, phenolic resins, and the like. As curing agents that can avoid affecting the viscosity of the epoxy resin and maintain the low viscosity of the main agent, catalytic tertiary amines, imidazoles, Lewis acids, and Bronsted bases are easy to operate. Specific examples include borate-based cationic polymerizers, SI series manufactured by Sun-Aid (registered trademark), etc. which are useful.

[0121] [Regarding metal particles] As the metal particles added to the resin composition according to the embodiment, metal particles generally used as small particle size fillers can be widely used. For example, the metal particles include a substance composed of at least one of Au, Ag, Pt, Cu, Cr, Zr, Zn, Ta, Ti, Mg, Ni, Ca, Ba, Al, Y, Hf, Ce, Ti, Mo, W, Si, Pd, Ir, Sn, Fe, Pb, Pd, Nd. The average particle diameter (average primary particle diameter) of the metal particles is typically in the range of 1.0 μm or more and 4 μm or less from the viewpoint of suppressing the variation in the viscosity of the acoustic matching layer composition and the variation in acoustic impedance between each array oscillator as described above. The metal particle material and each content are appropriately adjusted within the range of 2.3 ≦ Z / √ρ ≦ 2.9 with respect to the designed acoustic impedance Z. The metal particles may contain 5% by volume or less of particles having a particle diameter of 2.0 μm or less or 0.005 μm or more.

[0122] [Regarding the mixing ratio of resin and metal particles] The epoxy content in the layer material of the embodiment is preferably 60 to 80% by mass. Also, the metal particle content in the layer material of the embodiment is preferably 20 to 40% by mass. That is, typically, the content of metal particles in the resin composition is 20% by volume or more and 40% by volume or less.

[0123] [Regarding the mixing process of resin and metal particles] The points to note regarding the mixing process of resin and metal particles are as follows. That is, first, each component can be uniformly mixed; second, the entrained air can be properly degassed; and third, mixing under low-temperature conditions that can suppress the start of the heat-curing reaction is noted. As a mixing method, for example, kneading can be performed using a planetary mixer with a vacuum degassing mechanism.

[0124] [Regarding the coating process] The acoustic matching layer composition purified by the above method is coatable. Examples of specific coating methods include slit coating and coating with an applicator. Taking coating with an applicator as an example, the thickness of the matching layer can be controlled by the gap of the applicator and the coating speed.

[0125] Note that the configuration of the matching layer is not limited to a single layer. For example, after finishing the coating of the first layer, by changing the gap of the applicator, the second matching layer can be coated on the first coated matching layer, and the third matching layer can be coated on the second coated matching layer, and so on. With such a configuration, it is possible to laminate and coat an acoustic matching layer composition having a plurality of acoustic impedances without using an adhesive. Also, the coated matching layer can be heat-cured in a clean oven to obtain a sheet-like single-layer or multi-layer acoustic matching sheet.

[0126] [Regarding the curing method] Next, the curing method after applying the resin matching layer will be mentioned. The curing shrinkage that occurs when the resin matching layer cures and the linear expansion that occurs in the heating process are the causes of the warping of the resin matching layer. Therefore, the use of room temperature curing resins or UV curing resins is recommended. However, for example, when a room temperature curing resin is used, the temperature rises due to the contact and frictional heat between the fillers during the mixing process of the resin and the filler, and the polymerization reaction starts and cures. Also, when a photocuring resin is used, curing unevenness occurs in the depth direction because the filler absorbs and scatters light.

[0127] Therefore, we examined the curing method after applying the resin matching layer. As a result, even when using a heat-curing resin (cured at 150 °C), a high-precision coating process that does not induce warping of the resin acoustic matching layer was established.

[0128] Hereinafter, specific embodiments will be described from the first example of the second embodiment to the third example of the second embodiment. In the first example of the second embodiment, the case where copper is selected as the metal particles will be described. In the second example of the second embodiment, the case where tungsten is selected as the metal particles will be described. In the third example of the second embodiment, an example in the case where the acoustic matching layer is made into two layers will be described.

[0129] (First example of the second embodiment) In the first example of the second embodiment, the case of using copper (Cu) as the metal particles added to the resin is described assuming the case of creating an ultrasonic probe 1 with a center frequency of 20 - 30 MHz.

[0130] [Regarding the selection of metal particles] First, the reason for selecting copper (Cu) as the metal particles added to the resin when creating an ultrasonic probe 1 with a center frequency of 20 - 30 MHz will be explained.

[0131] As factors related to the acoustic matching layer, the design value of the acoustic impedance was set to Z = 7.6 [MRayl], the design value of the film thickness of the acoustic matching layer 20 was set to 30 μm, and the design value of the element size 27 was set to 40 μm.

[0132] Also, as a constraint condition, the attenuation coefficient of the acoustic matching layer composition generated by the reflection and scattering of the filler was set to be less than 0.6 dB / MHz / mm under a central frequency of 20 - 30 MHz. Under the above design values and constraint conditions, the achievable composition of the metal particles was examined.

[0133] Here, based on the relational expression 2.3 ≦ Z / √ρ ≦ 2.9 between the acoustic impedance Z and the density ρ of the metal particles as the filler to be added, the composition calculation was performed at Z / √ρ = 2.55 which is the intermediate value of these relational expressions. Substituting the design value of the acoustic impedance Z = 7.6 [MRayl], ρ = [8.883 g·cm^3] is obtained. In the first embodiment, considering various conditions such as being a material group generally used as a small particle size filler having a density close to this value, copper (Cu: ρ = [8.96 g·cm^3]) was selected.

[0134] [Regarding the particle size of the metal particles] Next, when examining the particle size of the metal particles as the filler to be added, the upper limit value of the particle size of the particles directly affects the variation in the acoustic characteristics of each array element if there are defects with a size of 10% or more with respect to the matching layer film thickness and the element size. Therefore, it is desirable that the upper limit value of the particle size of the particles does not exceed 10% of the matching layer film thickness and the element size. Considering that the design value of the matching layer film thickness is 30 μm and the design value of the element size is 40 μm, the particle size of the metal particles as the filler to be added is desirably 3 μm or less.

[0135] Based on the above examination, in the first example of the second embodiment, a commercially available material of Cu (ρ = [8.96 g·cm^3]) with an average particle size of 2.1 μm was selected as the metal particles to be added in the first example of the second embodiment.

[0136] [Regarding the resin] Next, the resin to be mixed with the metal particles will be described. As the resin to be mixed with the metal particles, for example, an epoxy resin can be considered. In the first example of the second embodiment, as the epoxy resin to be mixed with the metal particles, an aliphatic cyclic (alicyclic) epoxy resin, for example, Celoxide 2021P (registered trademark) of Daicel Corporation (registered trademark), was selected. This material is a liquid epoxy resin with a low viscosity (250 mPas @ 24°C) and is suitable for the acoustic matching layer composition for coating purposes.

[0137] [Regarding the mixing ratio of resin and metal particles] Subsequently, the mixing amount of the resin and the metal particles will be described. By appropriately adjusting the mixing ratio of the resin and the metal particles, the value of the acoustic impedance Z can be adjusted. Substituting the density ρ of copper, ρ = [8.96 g·cm^3], into the relational expression 2.3 ≦ Z / √ρ ≦ 2.9 between the acoustic impedance Z and the density ρ of the metal particles as the filler to be added, 6.88 < Z < 8.68 [MRayl] is obtained. Therefore, by changing the mixing amount of the resin and the metal particles, the value of the acoustic impedance Z can be adjusted. In the example, when the addition of the metal particles as the filler in epoxy + hardener + filler was 33 vol% by volume ratio, the acoustic impedance Z of the obtained resin composition was Z = 7.6 [MRayl].

[0138] [Regarding the hardener] Next, the hardener will be described. As the hardener, a borate-based cationic polymerizer can be considered. In the example, SI-B3A (registered trademark) manufactured by Sun-Aid (registered trademark) was added at 0.15 vol%. Note that adding the hardener in solid form is difficult for uniform dispersion in the resin. For example, the hardener was diluted with acetone, added so that the addition amount of the hardener became 0.15 vol%, and the acetone was removed by vacuum degassing.

[0139] [Regarding the mixing process of resin and metal particles] Next, the mixing process of the resin, metal particles as the filler, and the curing agent will be described. An example of such a mixing flow is shown in FIG. 9. As for the mixing of the resin, metal particles, and curing agent, for example, it is conceivable to perform the mixing using a planetary stirrer with a vacuum degassing mechanism.

[0140] Specifically, first, 18 g of Celloxide 2021P (registered trademark) of Daicel Corporation (registered trademark) was weighed as the epoxy resin (first step). Subsequently, 73.5 g of copper filler was weighed (second step). Subsequently, the copper filler, which is the metal particles weighed in the second step, and Celloxide 2021P (registered trademark) weighed in the first step were uniformly dispersed at 2000 rpm for 2 minutes (third step). Subsequently, after confirming the uniform dispersion, the fine bubbles mixed in were removed by stirring at 1000 rpm for 6 minutes again under a vacuum of 0.2 Pa (fourth step). Subsequently, the mixed solution of the copper filler and Celloxide 2021P heated by the high-speed rotation treatment was cooled to 25°C (room temperature) (fifth step). Subsequently, the planetary stirrer heated by the high-speed rotation treatment was cooled to 25°C (room temperature) (sixth step).

[0141] Subsequently, 0.15 vol% of the initiator: SI-B3A was dissolved in an acetone solution and added to the composition obtained in the sixth step (seventh step). Note that Stabilier and Retarder may be adjusted according to the situation. Subsequently, in order to suppress the temperature rise of the mixed solution during rotation, it was stirred in a vacuum at a low rotation speed (500 rpm) for 1 minute to remove the residual solvent and fine bubbles (eighth step). Subsequently, it was stirred in a vacuum at the core at 200 rpm for 15 minutes (ninth step). Subsequently, after confirming visually that there was no degassing from the surface of the mixed solution (tenth step), the mixed composition was transferred to a dispensing syringe (eleventh step). Subsequently, the mixed solution of the copper filler and Celloxide 2021P (registered trademark) heated by the high-speed rotation treatment was cooled to 25°C (twelfth step). Subsequently, the planetary stirrer heated by the high-speed rotation treatment was cooled to 25°C (room temperature) with a cooling jig (thirteenth step). Subsequently, the bubbles remaining in the syringe were stirred in a vacuum at the core at 200 rpm for 4 minutes (fourteenth step).

[0142] Through the above process, it becomes possible to mix the copper filler after adding SI-B3A, which is the starting material, and Celloxide 2021P (registered trademark) at 35°C or lower. By enabling mixing at low temperatures, it becomes possible to suppress the start of the polymerization reaction and suppress the viscosity change (pot life) of the acoustic matching layer composition.

[0143] In the slit coating and applicator coating processes, the viscosity change of the composition directly affects the coating film thickness, so it is not desirable from the perspective of film thickness controllability. When a matching layer with a designed matching layer film thickness of 40 μm was formed by coating, it was confirmed that the viscosity increase rate of the current mixing process was less than 10% one hour after the initiator was added, and the coating film thickness fluctuation amount was controllable within less than +0.2 μm.

[0144] Also, as described above, the acoustic matching layer composition can be adjusted within the range of the relational expression 2.3 ≦ Z / √ρ ≦ 2.9 of the designed acoustic impedance and the filler density in accordance with the designed impedance. That is, when a copper filler with ρ = [8.96 g·cm^3] is selected, an acoustic matching layer composition in the range of 6.88 < Z < 8.68 [MRayl] can be formed with respect to the acoustic impedance Z. The experimental results of changing the designed acoustic impedance of the acoustic matching layer composition using a copper filler are shown in FIG. 10.

[0145] A list of the composition and evaluation results for the designed impedance is shown. In the composition region (Z = 6.9 [MRayl]) of the low viscosity region 42 shown in FIG. 8, sedimentation of the filler occurred, and the filler was not uniformly dispersed on the outermost surface, and a thin film layer of only epoxy was formed, indicating that it was impossible to operate as an acoustic matching layer composition. On the other hand, in the composition region (Z = 10.0 [MRayl]) of the high viscosity region 43 shown in FIG. 8, due to the high viscosity, precise coating with a designed film thickness t = 40 μm (coating error < + / −1 μm) was impossible with the slit coating or applicator coating methods. Note that since substrates with thicknesses of 1 mm, 2 mm, and 3 mm are used for the acoustic impedance measurement samples, formation and measurement are possible even with a material having a certain degree of high viscosity.

[0146] (Second Example of the Second Embodiment) In the second example of the second embodiment, when assuming the case of creating an ultrasonic probe 1 with a center frequency of about 30 MHz, the case of using tungsten (W) as the metal particles added to the resin will be described.

[0147] [Regarding the selection of metal particles] First, the reason for selecting tungsten (W) as the metal particles added to the resin when creating an ultrasonic probe 1 with a center frequency of about 30 MHz will be described.

[0148] As factors related to the acoustic matching layer, the design value of the acoustic impedance was set to Z = 11.2 [MRayl] close to the glass matching layer, the design value of the film thickness of the acoustic matching layer 20 was set to 40 μm, and the design value of the element size 24 was set to 40 μm.

[0149] Also, as a constraint condition, the attenuation coefficient of the acoustic matching layer composition generated by the reflection and scattering of the filler was set to less than 0.6 dB / MHz / mm under a center frequency of 20 - 30 MHz. Under the above design values and constraint conditions, the achievable composition of the metal particles was examined.

[0150] Here, based on the relational expression 2.3 ≦ Z / √ρ ≦ 2.9 between the acoustic impedance Z and the density ρ of the metal particles as the filler to be added, composition calculation was performed at Z / √ρ = 2.55 which is the intermediate value of these relational expressions. Substituting the design value of the acoustic impedance Z = 11.2 [MRayl], ρ = [19.291 g·cm^3] is obtained. In the second example of the second embodiment, considering various conditions such as being a material group generally used as a small particle size filler having a density close to this value, tungsten (W: ρ = [19.3 g·cm^3]) was selected.

[0151] [Regarding the particle size of metal particles] Next, considering the particle size of the metal particles, which are the fillers to be added, if the upper limit value of the particle size is such that there are defects with a size of 10% or more relative to the thickness of the matching layer or the element size, it will directly affect the variation in the acoustic characteristics of each array element. Therefore, it is desirable that the upper limit value of the particle size does not exceed 10% of the thickness of the matching layer or the element size. From this, considering that the designed value of the thickness of the matching layer is 40 μm and the designed value of the element size is 40 μm, the particle size of the metal particles, which are the fillers to be added, is desirably 4 μm or less.

[0152] Based on the above considerations, in the second example of the second embodiment, W with an average particle size of 2.2 μm (a commercially available material with ρ = [19.3 g·cm^3]) was selected as the metal particles to be added in the second example of the second embodiment.

[0153] [Regarding the resin] Next, the resin to be mixed with the metal particles will be described. As the resin to be mixed with the metal particles, for example, an epoxy resin can be considered. In the second example of the second embodiment, as the epoxy resin to be mixed with the metal particles, an aliphatic cyclic (alicyclic) epoxy resin, for example, Celoxide 2021P (registered trademark) of Daicel Corporation (registered trademark), was selected. This material is a liquid epoxy resin with a low viscosity (250 mPas @ 24°C) and is suitable for the acoustic matching layer composition for coating purposes.

[0154] [Regarding the mixing ratio of the resin and the metal particles] Next, the mixing amount of the resin and the metal particles will be described. By appropriately adjusting the mixing ratio of the resin and the metal particles, the value of the acoustic impedance Z can be adjusted. Substituting the density ρ of tungsten, ρ = [19.3·cm^3], into the relational expression 2.3 ≦ Z / √ρ ≦ 2.9 between the acoustic impedance Z and the density ρ of the metal particles as the filler to be added, 10.1 < Z < 12.7 [MRayl] is obtained. Therefore, by changing the mixing amount of the resin and the metal particles, the value of the acoustic impedance Z can be adjusted. In the example, when the addition of the metal particles as the filler in epoxy + hardener + filler was 33.2 vol% in terms of volume ratio, the acoustic impedance Z of the obtained resin product was Z = 11.2 [MRayl].

[0155] [Regarding the hardener] Next, the hardener will be described. As the hardener, it is conceivable to use a borate-based cationic polymerizing agent. In the example, SI-B3A (registered trademark) manufactured by Sun-Aid (registered trademark) was added at 0.15 vol%. This is because it is difficult to uniformly disperse the addition of the solid hardener in the resin. For example, the hardener was diluted with acetone, added so that the addition amount of the hardener became 0.15 vol%, and the acetone was removed by vacuum degassing.

[0156] [Regarding the mixing process of the resin and the metal particles] Subsequently, the mixing process of the resin, the metal particles as the filler, and the hardener will be described. This is common to the first example of the second embodiment, and FIG. 9 shows an example of the mixing flow in the second example of the second embodiment. For the mixing of the resin, the metal particles, and the hardener, for example, it is conceivable to perform the mixing using a rotation-revolution stirrer with a vacuum degassing mechanism.

[0157] Specifically, first, 18 g of Celoxide 2021P (registered trademark) of Daicel Corporation was weighed as the epoxy resin (first step). Subsequently, 145 g of tungsten filler was weighed (second step). Subsequently, the tungsten filler, which is the metal particles weighed in the second step, and Celoxide 2021P (registered trademark) weighed in the first step were uniformly dispersed at 2000 rpm for 2 minutes (third step). Subsequently, after confirming the uniform dispersion, the fine bubbles mixed by stirring at 1000 rpm for 6 minutes were removed by evacuating to 0.2 Pa (fourth step). Subsequently, the mixed solution of the tungsten filler and Celoxide 2021P heated by high-speed rotation treatment was cooled to 25°C (room temperature) (fifth step). Subsequently, the revolving and orbiting stirrer heated by high-speed rotation treatment was cooled to 25°C (room temperature) (sixth step).

[0158] Subsequently, 0.15 vol% of the initiator: SI-B3A was dissolved in an acetone solution and added to the composition obtained in the sixth step (seventh step). Note that Stabilizer and Retarder may be adjusted according to the situation. Subsequently, in order to suppress the temperature rise of the mixed solution during rotation, it was stirred in a vacuum at a low rotation speed (500 rpm) for 1 minute to remove the residual solvent and fine bubbles (eighth step). Subsequently, it was stirred in a vacuum at 200 rpm for 15 minutes for nucleation (ninth step). Subsequently, after confirming visually that there was no defoaming from the surface of the mixed solution (tenth step), the mixed composition was transferred to a syringe for dispensing (eleventh step). Subsequently, the mixed solution of the tungsten filler and Celoxide 2021P (registered trademark) heated by high-speed rotation treatment was cooled to 25°C (twelfth step). Subsequently, the revolving and orbiting stirrer heated by high-speed rotation treatment was cooled to 25°C (room temperature) with a cooling jig (thirteenth step). Subsequently, the bubbles remaining in the syringe were stirred in a vacuum at 200 rpm for 4 minutes for nucleation (fourteenth step).

[0159] Through the above steps, it becomes possible to mix the tungsten filler and Celoxide 2021P (registered trademark) after adding SI-B3A, which is the starting material, at 35°C or lower. By enabling mixing at a low temperature, it becomes possible to suppress the start of the polymerization reaction and suppress the viscosity change (pot life) of the acoustic matching layer composition.

[0160] In the slit coating or applicator coating process, the viscosity change of the composition directly affects the coating film thickness, which is undesirable from the viewpoint of film thickness controllability. When a matching layer with a designed film thickness of 40 μm was formed by coating, it was confirmed that the viscosity increase rate of the current mixing process was less than 10% within 1 hour after the initiator was added, and the coating film thickness variation was controllable within less than +0.2 μm.

[0161] Also, as described above, the acoustic matching layer composition can be adjusted within the range of the relational expression 2.3 ≦ Z / √ρ ≦ 2.9 of the above-described designed acoustic impedance and filler density in accordance with the designed impedance. That is, when a tungsten filler with ρ = [19.3 g·cm^3] is selected, an acoustic matching layer composition in the range of 10.1 < Z < 12.7 [MRayl] can be formed for the acoustic impedance Z. The experimental results of changing the designed acoustic impedance of the acoustic matching layer composition using a tungsten filler are shown in FIG. 11.

[0162] A list of the composition and evaluation results for the designed impedance is shown. In the composition region (Z = 9.0 [MRayl]) of the low viscosity region 1042 shown in FIG. 8, sedimentation of the filler occurred and the filler was not uniformly dispersed in the outermost layer, and a thin film layer of only epoxy was formed, and it was found that it was impossible to operate as an acoustic matching layer composition. On the other hand, in the composition region (Z = 13.4 [MRayl]) of the high viscosity region 1043 shown in FIG. 8, due to the high viscosity, precise coating with a designed film thickness t = 40 μm (coating error < + / −1 μm) was impossible with the slit coating or applicator coating method. In addition, since substrates with thicknesses of 1 mm, 2 mm, and 3 mm are used for the acoustic impedance measurement samples, formation and measurement are possible even with a material having a certain degree of high viscosity.

[0163] (Third Example of the Second Embodiment) In the first and second examples of the second embodiment, the case of manufacturing a single-layer matching layer was described. However, the embodiment is not limited to this, and it may be the case of manufacturing an acoustic matching layer composed of a plurality of layers. In the third example of the second embodiment, the case where the acoustic matching layer is composed of a plurality of layers, for example, a two-layer matching layer, will be described. When the acoustic matching layer is composed of a plurality of layers, for example, after the coating of the first layer is completed, by changing the gap of the applicator, the second layer matching layer is coated on the first layer coating matching layer, and then the third layer matching layer is coated on the second layer coating matching layer, etc. By performing such processes, it becomes possible to perform laminated coating of an acoustic matching layer composition having a plurality of acoustic impedances without using an adhesive.

[0164] FIG. 12 shows a partial configuration of an ultrasonic oscillator unit in the case where the acoustic matching layer is a two-layer matching layer.

[0165] In the third example of the second embodiment, the acoustic matching layer 1020 is composed of a first acoustic matching layer 1020a and a second acoustic matching layer 1020b. That is, the ultrasonic oscillator unit 1070 is composed of a flexible wiring board 1022, a piezoelectric element 1021, a first acoustic matching layer 1020a, and a second acoustic matching layer 1020b. The element size 1027 of each ultrasonic oscillator 1071 in the ultrasonic oscillator unit 1070 is, for example, 40 μm. The thickness of the piezoelectric element 1021 is, for example, 40 μm. The thickness of the first acoustic matching layer 1020a is, for example, 40 μm. Also, the thickness of the second acoustic matching layer 1020b is, for example, 30 μm.

[0166] Here, the first acoustic matching layer 1020a is an acoustic matching layer created by adding metal particles, for example, tungsten, to a resin. Also, the second acoustic matching layer 1020b is an acoustic matching layer created by adding ceramic particles, for example, aluminum oxide, to a resin.

[0167] Note that the embodiments are not limited to this. For example, the order of the first acoustic matching layer 1020a and the second acoustic matching layer 1020b may be reversed, and the materials of the first acoustic matching layer 1020a and the second acoustic matching layer 1020b may be other than those described above.

[0168] [Regarding the selection of metal particles in the first acoustic matching layer 1020a] Regarding the first acoustic matching layer 1020a, based on the following considerations, tungsten (W) was used as the metal particles to be added to the resin.

[0169] As factors related to the acoustic matching layer, the designed value of the acoustic impedance was set to Z = 11.2 [MRayl], the designed value of the film thickness of the first acoustic matching layer 1020a was set to 40 μm, and the designed value of the element size 24 was set to 40 μm.

[0170] Also, as a constraint condition, the attenuation coefficient of the acoustic matching layer composition generated by the reflection and scattering of the filler was set to less than 0.6 dB / MHz / mm at a center frequency of 20 - 30 MHz. Under the above designed values and constraint conditions, the achievable composition of metal particles was examined.

[0171] Here, based on the relational expression 2.3 ≦ Z / √ρ ≦ 2.9 between the acoustic impedance Z and the density ρ of the metal particles as the filler to be added, composition calculations were performed at Z / √ρ = 2.55, which is the intermediate value of these relational expressions. Substituting the designed value of the acoustic impedance Z = 11.2 [MRayl], we get ρ = [19.291 g·cm^3]. Considering various conditions such as being a material group commonly used as a small particle size filler with a density close to this value, tungsten (W: ρ = [19.3 g·cm^3]) was selected.

[0172] [Regarding the particle size of the metal particles in the first acoustic matching layer 1020a] Next, considering the particle size of the metal particles, which are the fillers to be added, if the upper limit value of the particle size of the particles is such that there are defects with a size of 10% or more with respect to the thickness of the matching layer or the element size, it directly affects the variation in the acoustic characteristics of each array element. Therefore, it is desirable that the upper limit value of the particle size of the particles does not exceed 10% of the thickness of the matching layer or the element size. From this, considering that the designed value of the thickness of the matching layer is 40 μm and the designed value of the element size is 40 μm, the particle size of the metal particles, which are the fillers to be added, is desirably 4 μm or less.

[0173] Based on the above considerations, in the third embodiment of the second embodiment, commercially available W (ρ = [19.3 g·cm^3]) with an average particle size of 2.2 μm was selected as the metal particles to be added in the third embodiment of the second embodiment.

[0174] [Regarding the first acoustic matching layer 1020a: Resin] Next, the resin to be mixed with the metal particles will be described. As the resin to be mixed with the metal particles, for example, an epoxy resin can be considered. Specifically, as the epoxy resin to be mixed with the metal particles, an aliphatic cyclic (alicyclic) epoxy resin, for example, Celoxide 2021P (registered trademark) of Daicel Corporation (registered trademark) was selected. This material is a liquid epoxy resin with a low viscosity (250 mPas @ 24°C) and is suitable for an acoustic matching layer composition for coating purposes.

[0175] [Regarding the first acoustic matching layer 1020a: Mixing ratio of resin and metal particles] Next, the mixing amount of the resin and the metal particles will be described. By appropriately adjusting the mixing ratio of the resin and the metal particles, the value of the acoustic impedance Z can be adjusted. Substituting the density ρ of tungsten, ρ = [19.3·cm^3], into the relational expression 2.3 ≦ Z / √ρ ≦ 2.9 between the acoustic impedance Z and the density ρ of the metal particles as the filler to be added, 10.1 < Z < 12.7 [MRayl] is obtained. Therefore, by changing the mixing amount of the resin and the metal particles, the value of the acoustic impedance Z can be adjusted. In the example, when the addition of the metal particles as the filler in epoxy + hardener + filler was 33.2 vol% in terms of volume ratio, the acoustic impedance Z of the obtained resin composition was Z = 11.2 [MRayl].

[0176] [First acoustic matching layer 1020a: Regarding the hardener] Next, the hardener will be described. As the hardener, a borate-based cationic polymerizing agent can be considered for use. In the example, SI-B3A (registered trademark) manufactured by Sun-Aid (registered trademark) was added at 0.15 vol%. Note that since it is difficult to uniformly disperse the addition of the hardener in a solid state. For example, the hardener was diluted with acetone, added so that the addition amount of the hardener became 0.15 vol%, and the acetone was removed by vacuum degassing.

[0177] [First acoustic matching layer 1020a: Regarding the mixing process of the resin and the metal particles] Subsequently, the mixing process of the resin, the metal particles as the filler, and the hardener will be described. As described above, an example of such a mixing flow is shown in FIG. 9. As for the mixing of the resin, the metal particles, and the hardener, for example, it is conceivable to perform the mixing using a rotation-revolution stirrer equipped with a vacuum degassing mechanism.

[0178] Specifically, first, 18 g of Celoxide 2021P (registered trademark) of Daicel Corporation (registered trademark) was weighed as the epoxy resin (first step). Subsequently, 145 g of tungsten filler was weighed (second step). Subsequently, the tungsten filler, which is the metal particles weighed in the second step, and Celoxide 2021P (registered trademark) weighed in the first step were uniformly dispersed at 2000 rpm for 2 minutes (third step). Subsequently, after confirming the uniform dispersion, the fine bubbles mixed by stirring again at 1000 rpm for 6 minutes with a vacuum of 0.2 Pa were removed (fourth step). Subsequently, the mixed solution of tungsten filler and Celoxide 2021P heated by high-speed rotation treatment was cooled to 25 °C (room temperature) (fifth step). Subsequently, the planetary mixer heated by high-speed rotation treatment was cooled to 25 °C (room temperature) (sixth step).

[0179] Subsequently, 0.15 vol% of initiator: SI-B3A was dissolved in an acetone solution and added to the composition obtained in the sixth step (seventh step). Note that Stabilizer and Retarder may be adjusted according to the situation. Subsequently, in order to suppress the temperature rise of the mixed solution during rotation, it was stirred in a vacuum at low speed (500 rpm) for 1 minute to remove the residual solvent and fine bubbles (eighth step). Subsequently, it was nuclearly stirred in a vacuum at 200 rpm for 15 minutes (ninth step). Subsequently, after confirming visually that there was no defoaming from the surface of the mixed solution (tenth step), the mixed composition was transferred to a dispensing syringe (eleventh step). Subsequently, the mixed solution of tungsten filler and Celoxide 2021P (registered trademark) heated by high-speed rotation treatment was cooled to 25 °C (twelfth step). Subsequently, the planetary mixer heated by high-speed rotation treatment was cooled to 25 °C (room temperature) with a cooling jig (thirteenth step). Subsequently, the bubbles remaining in the syringe were nuclearly stirred in a vacuum at 200 rpm for 4 minutes (fourteenth step).

[0180] Through the above steps, it becomes possible to mix the tungsten filler and Celoxide 2021P (registered trademark) after adding SI-B3A, which is the starting material, at 35 °C or lower. By enabling mixing at low temperatures, it becomes possible to suppress the start of the polymerization reaction and suppress the viscosity change (pot life) of the acoustic matching layer composition.

[0181] In the slit coating or applicator coating process, the viscosity change of the composition directly affects the coating film thickness, which is not desirable from the perspective of film thickness controllability. When a matching layer with a designed film thickness of 40 μm was formed by coating, it was confirmed that the viscosity increase rate of the current mixing process was less than 10% one hour after the initiator was added, and the coating film thickness variation was controllable within less than +0.2 μm.

[0182] [Second Acoustic Matching Layer 1020b: Selection of Ceramic Particles] In the second acoustic matching layer 1020b, ceramic particles were used as the substance added to the resin. Specifically, aluminum oxide (Al2O3) was selected.

[0183] As factors related to the acoustic matching layer, the designed value of the acoustic impedance was set to Z = 5.6 [MRayl], the designed value of the film thickness of the acoustic matching layer 1020b was 30 μm, and the designed value of the element size 1024 was 40 μm.

[0184] Also, as a constraint condition, the attenuation coefficient of the acoustic matching layer composition generated by the reflection and scattering of the filler was set to less than 0.6 dB / MHz / mm at a center frequency of 20 - 30 MHz. Under the above design values and constraint conditions, the achievable ceramic particle composition was investigated.

[0185] Here, based on the relational expression 2.3 ≦ Z / √ρ ≦ 3.4 between the acoustic impedance Z and the density ρ of the ceramic particles as the filler to be added, composition calculations were performed at Z / √ρ = 2.85, which is the intermediate value of these relational expressions. Substituting the designed value of the acoustic impedance Z = 5.6 [MRayl], ρ = [3.99 g·cm^3] is obtained. In the first embodiment, considering various conditions such as being a small particle filler having a density close to this value and being a group of commonly used ceramic materials, aluminum oxide (Al2O3: ρ = [3.8 g·cm^3]) was selected.

[0186] [Second Acoustic Matching Layer 1020b: Particle Size of Ceramic Particles] Next, considering the particle size of the ceramic particles as the filler to be added, the upper limit value of the particle size of the particles should not exceed 5% of the thickness of the matching layer or the element size, because if there are defects with a size of 5% or more with respect to the matching layer thickness or the element size, it will directly affect the variation in the acoustic characteristics of each array element. Therefore, considering that the designed value of the matching layer thickness is 30 μm and the designed value of the element size is 40 μm, the particle size of the ceramic particles as the filler to be added is desirably 1.5 μm or less.

[0187] Based on the above considerations, commercially available Al2O3 with an average particle size of 0.7 μm (ρ = [3.8 g·cm^3]) was selected as the ceramic particles to be added to the second acoustic matching layer 1020b. Substituting the filler density ρ = [3.8 g·cm^3] into the relational expression 2.3 ≦ Z / √ρ ≦ 3.4 for the acoustic impedance Z and the density ρ of the ceramic particles as the filler to be added, we get 4.48 < Z < 6.63 [MRayl]. Therefore, the acoustic impedance Z can be changed within this range.

[0188] [Second acoustic matching layer 1020b: Regarding the resin] Next, the resin to be mixed with the ceramic particles will be described. As the resin to be mixed with the ceramic particles, for example, an epoxy resin can be considered. As the epoxy resin to be mixed with the ceramic particles, for example, Celoxide 2021P (registered trademark) of Daicel Corporation (registered trademark) was selected. This material is a liquid epoxy resin with a low viscosity (250 mPas @ 24°C) and is suitable for the acoustic matching layer composition for coating purposes.

[0189] [Second acoustic matching layer 1020b: Regarding the mixing ratio of the resin and the ceramic particles] Next, the mixing amount of the resin and the ceramic particles will be described. By appropriately adjusting the mixing ratio of the resin and the ceramic particles, the value of the acoustic impedance Z can be adjusted. Substituting the density ρ = [3.8 g·cm^3] of Al2O3 into the relational expression 2.3 ≦ Z / √ρ ≦ 3.4 between the acoustic impedance Z and the density ρ of the ceramic particles as the filler to be added, 4.48 < Z < 6.63 [MRayl] is obtained. Therefore, by changing the mixing amount of the resin and the ceramic particles, the value of the acoustic impedance Z can be adjusted. In the example, when the addition of the ceramic particles as the filler in epoxy + hardener + filler was 30 vol% in terms of volume ratio, the acoustic impedance Z of the obtained resin composition was Z = 5.6 [MRayl].

[0190] [Second acoustic matching layer 1020b: Regarding the hardener] Next, the hardener will be described. As the hardener, it is conceivable to use a borate-based cationic polymerizing agent. In the example, SI-B3A (registered trademark) manufactured by Sun-Aid (registered trademark) was added at 0.15 vol%. Since it is difficult to uniformly disperse the addition of the hardener in a solid state in the resin, for example, it is conceivable to dilute the hardener with acetone, add it so that the addition amount of the hardener becomes 0.15 vol%, and remove the acetone by vacuum degassing.

[0191] [Second acoustic matching layer 1020b: Regarding the mixing process of the resin and the ceramic particles] Subsequently, the mixing process of the resin, the ceramic particles as the filler, and the hardener will be described. As already described, an example of such a mixing flow is shown in FIG. 9. For the mixing of the resin, the ceramic particles, and the hardener, for example, it is conceivable to perform the mixing using a rotation-revolution stirrer equipped with a vacuum degassing mechanism.

[0192] Specifically, first, 18.6 g of Celoxide 2021P (registered trademark) of Daicel Corporation (registered trademark) was weighed as the epoxy resin (first step). Subsequently, 25.5 g of Al2O3 filler was weighed (second step). Subsequently, the Al2O3 filler, which is the ceramic particles weighed in the second step, and Celoxide 2021P (registered trademark) weighed in the first step were uniformly dispersed at 2000 rpm for 2 minutes (third step). Subsequently, after confirming the uniform dispersion, the fine bubbles mixed in by stirring again at 2000 rpm for 6 minutes under a vacuum of 0.2 Pa were removed (fourth step). Subsequently, the mixed solution of the Al2O3 filler and Celoxide 2021P heated by the high-speed rotation treatment was cooled to 25 °C (room temperature) (fifth step). Subsequently, the high-speed rotation treatment self-rotating and revolving stirrer heated was cooled to 25 °C (room temperature) with a cooling jig (sixth step).

[0193] Subsequently, 0.15 vol% of the curing agent: SI-B3A was dissolved in acetone and added to the composition obtained in the sixth step (seventh step). Subsequently, in order to suppress the temperature rise of the mixed solution during rotation, it was stirred in a vacuum at a low rotation speed (500 rpm) for 1 minute to remove the residual solvent and fine bubbles (eighth step). Subsequently, it was nuclearly stirred in a vacuum at 200 rpm for 15 minutes (ninth step). Subsequently, after confirming visually that there was no defoaming from the surface of the mixed solution (tenth step), the mixed composition was transferred to a dispensing syringe (eleventh step). Subsequently, the mixed solution of the Al2O3 filler and Celoxide 2021P (registered trademark) heated by the high-speed rotation treatment was cooled to 25 °C (twelfth step). Subsequently, the high-speed rotation treatment self-rotating and revolving stirrer heated was cooled to 25 °C (room temperature) with a cooling jig (thirteenth step). Subsequently, the bubbles remaining in the syringe were nuclearly stirred in a vacuum at 200 rpm for 4 minutes (fourteenth step).

[0194] Through the above steps, it becomes possible to mix the Al2O3 filler and Celoxide 2021P (registered trademark) after adding the curing agent at 35 °C or lower. Under the above mixing conditions, it becomes possible to control the pot life (viscosity change rate 2 hours after adding the curing agent) of the acoustic matching layer composition with Z = 5.6 [MRayl] to less than 5%.

[0195] In the slit coating or applicator coating process, the viscosity change of the composition directly affects the coating film thickness, which is undesirable from the perspective of film thickness controllability. When a matching layer with a designed matching layer film thickness of 30 μm was formed by coating, it was confirmed that when the viscosity increase rate of the current process was less than 5%, the variation in the coating film thickness could be controlled to less than +0.1 μm.

[0196] [Manufacture of two-layer matching layer] As described above, the manufacturing methods of the first matching layer 1020a and the second matching layer 1020b have been explained. Subsequently, the manufacturing method of the entire matching layer composition and the like will be described.

[0197] As an example of the manufacturing method of the matching layer composition, the preparation of the matching layer composition using an applicator can be considered. As an example, a method of coating the first matching layer 1020a and the second matching layer composition 1020b on a smooth substrate using an applicator to produce a sheet of the two-layer matching layer can be considered. Since the compositions have different viscosities and thixotropies, the coating film thickness varies with the coating speed and the gap of the applicator. As a result of examining the coating conditions of the matching layer composition, the first matching layer composition was coated on a smooth substrate at a gap of 70 μm and a coating speed of 10 mm / sec, and the second matching layer composition was continuously coated on the first matching layer at a gap of 110 μm and a coating speed of 5 mm / sec, heated and cured at 130 °C, and peeled off from the smooth substrate, so that it was possible to obtain a sheet of the two-layer matching layer with the first matching layer / second matching layer = 40 μm / 30 μm shown in FIG. 12. After adhering the obtained two-layer matching layer sheet to the piezoelectric element and then arraying it to an element size of 40 μm using a blade dicing machine, it is possible to obtain an ultrasonic array element including the two-layer matching shown in FIG. 12.

[0198] Regarding the above embodiments, the following supplementary notes are disclosed as one aspect and selective features of the invention

[0199] (Supplementary Note 1) The resin composition provided in one aspect of the present invention is A resin composition which is a precursor of an acoustic matching layer of an ultrasonic vibrator in an ultrasonic vibrator unit having an array vibrator including a piezoelectric body and an electrode, the resin composition contains a resin and ceramic particles, when the acoustic impedance of the acoustic matching layer is Z and the density of the ceramic particles is ρ, 2.3 ≦ Z / √ρ ≦ 3.4 is satisfied.

[0200] (Appendix 2) The Z may be in the range of 3.0 or more and 15 MRayl or less.

[0201] (Appendix 3) The particle size distribution of the average particle size of the ceramic particles may be a unimodal distribution.

[0202] (Appendix 4) The content of the ceramic particles in the resin composition may be 20% by volume or more and 40% by volume or less.

[0203] (Appendix 5) The average particle size of the ceramic particles may be 0.3 μm or more and 2 μm or less.

[0204] (Appendix 6) The ceramic particles may contain a substance composed of at least one of Mg, Ca, Ba, B, Al, Y, Hf, Ce, Ti, W, Si and at least one of O, C, N and S.

[0205] (Appendix 7) The ceramic particles may contain 5% by volume or less of particles having a particle size of 2.0 μm or less or 0.005 μm or more.

[0206] (Appendix 8) The resin may be an epoxy resin.

[0207] (Appendix 9) A thermosetting resin may be used as a curing agent for the epoxy resin.

[0208] (Supplementary Note 10) The ceramic particles may be aluminum oxide.

[0209] (Supplementary Note 11) The ceramic particles may be tungsten carbide.

[0210] (Supplementary Note 12) In one aspect of the present invention, the resin composition provided is a resin composition that is a precursor of an acoustic matching layer of an ultrasonic vibrator in an ultrasonic vibrator unit having an array vibrator including a piezoelectric body and an electrode, the resin composition contains a resin and metal particles, when the acoustic impedance of the acoustic matching layer is Z and the density of the metal particles is ρ, it satisfies 2.3 ≦ Z / √ρ ≦ 2.9.

[0211] (Supplementary Note 13) The Z may be in the range of 3.0 or more and 15 MRayl or less.

[0212] (Supplementary Note 14) The particle size distribution of the average particle size of the metal particles may be a unimodal distribution.

[0213] (Supplementary Note 15) The content of the metal particles in the resin composition may be 20% by volume or more and 40% by volume or less.

[0214] (Supplementary Note 16) The average particle size of the metal particles may be 1.0 μm or more and 4 μm or less.

[0215] (Supplementary Note 17) The metal particles may contain a substance composed of at least one of Au, Ag, Pt, Cu, Cr, Zr, Zn, Ta, Ti, Mg, Ni, Ca, Ba, Al, Y, Hf, Ce, Ti, Mo, W, Si, Pd, Ir, Sn, Fe, Pb, Pd, Nd.

[0216] (Supplementary Note 18) The metal particles may contain 5% by volume or less of particles having a particle size of 2.0 μm or less or 0.005 μm or more.

[0217] (Appendix 19) The resin may be an epoxy resin.

[0218] (Appendix 20) A thermosetting resin may be used as a curing agent for the epoxy resin.

[0219] (Appendix 21) The metal particles may be copper or tungsten.

[0220] According to at least one of the embodiments described above, a resin composition with low attenuation and capable of being applied can be produced.

[0221] Although several embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations of the embodiments can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and its equivalent scope.

Description of Reference Numerals

[0222] 20 Acoustic matching layer 21 Piezoelectric element 22 Flexible wiring board 23 Ultrasonic vibrator 1020 Acoustic matching layer 1020a First acoustic matching layer 1020b Second acoustic matching layer 1021 Piezoelectric element 1022 Flexible wiring board 1070 Ultrasonic vibrator unit 1071 Ultrasonic vibrator

Claims

1. A resin composition which is a precursor of an acoustic matching layer of an ultrasonic transducer in an ultrasonic transducer unit having an array transducer including a piezoelectric body and an electrode, The resin composition includes a resin and particles of an inorganic material, Assuming that the acoustic impedance of the acoustic matching layer is Z and the density of the particles of the inorganic material is ρ, then A resin composition satisfying 2.3≦Z / √ρ≦3.

4.

2. The resin composition according to claim 1 , wherein the particles of the inorganic material are ceramic particles.

3. The resin composition according to claim 1 , wherein Z is in the range of 3.0 to 15 MRayl.

4. The resin composition according to claim 2 , wherein the ceramic particles have an average particle size distribution that is a unimodal distribution.

5. The resin composition according to claim 2 , wherein the content of the ceramic particles in the resin composition is 20% by volume or more and 40% by volume or less.

6. 3. The resin composition according to claim 2, wherein the ceramic particles have an average particle size of 0.3 μm or more and 2 μm or less.

7. The resin composition according to claim 2, wherein the ceramic particles contain a substance composed of at least one of Mg, Ca, Ba, B, Al, Y, Hf, Ce, Ti, W, and Si, and at least one of O, C, N, and S.

8. The resin composition according to claim 2 , wherein the ceramic particles contain 5% by volume or less of particles having a particle size of 2.0 μm or less or 0.005 μm or more.

9. The resin composition according to claim 1 , wherein the resin is an epoxy resin.

10. The resin composition according to claim 9, wherein a thermosetting resin is used as a curing agent for the epoxy resin.

11. The resin composition according to claim 2 , wherein the ceramic particles are aluminum oxide.

12. The resin composition according to claim 2 , wherein the ceramic particles are tungsten carbide.

13. the inorganic particles are metal particles, Assuming that the acoustic impedance of the acoustic matching layer is Z and the density of the metal particles is ρ, The resin composition according to claim 1, wherein 2.3≦Z / √ρ≦2.9 is satisfied.

14. The resin composition according to claim 13, wherein the particle size distribution of the average particle size of the metal particles is a unimodal distribution.

15. The resin composition according to claim 13, wherein the content of the metal particles in the resin composition is 20% by volume or more and 40% by volume or less.

16. The resin composition according to claim 13, wherein the average particle size of the metal particles is 1.0 μm or more and 4 μm or less.

17. The resin composition according to claim 13, wherein the metal particles include a substance composed of at least one of Au, Ag, Pt, Cu, Cr, Zr, Zn, Ta, Ti, Mg, Ni, Ca, Ba, Al, Y, Hf, Ce, Ti, Mo, W, Si, Pd, Ir, Sn, Fe, Pb, Pd, and Nd.

18. The resin composition according to claim 13, wherein the metal particles contain 5% by volume or less of particles having a particle size of 2.0 μm or less or 0.005 μm or more.

19. The resin composition according to claim 13, wherein the metal particles are copper or tungsten.

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