Patent Description:
In the acoustic wave measurement apparatus, an acoustic wave probe is used which irradiates a test object or a site (hereinafter, simply referred to as an object) with an acoustic wave, receives a reflected wave (echo) thereof, and outputs a signal. An electrical signal converted from the reflected wave which has been received by this acoustic wave probe is displayed as an image. Accordingly, the interior of the test object is visualized and observed.

Acoustic waves, such as ultrasonic waves and photoacoustic waves, which have an appropriate frequency in accordance with a test object and/or measurement conditions, are selected as the acoustic waves.

For example, the ultrasound diagnostic apparatus transmits an ultrasonic wave to the interior of a test object, receives the ultrasonic wave reflected by the tissues inside the test object, and displays the received ultrasonic wave as an image. The photoacoustic wave measurement apparatus receives an acoustic wave radiated from the interior of a test object due to a photoacoustic effect, and displays the received acoustic wave as an image. The photoacoustic effect is a phenomenon in which an acoustic wave (typically an ultrasonic wave) is generated through thermal expansion after a test object absorbs an electromagnetic wave and generates heat in a case where the test object is irradiated with an electromagnetic wave pulse of e.g. visible light, near infrared light or microwave.

The acoustic wave measurement apparatus performs transmission and reception of an acoustic wave on a living body (typically, the human body) which is a test object. Therefore, it is necessary to fulfill requirements such as consistency in the acoustic impedance within the living body and/or decrease in acoustic attenuation.

For example, a probe for an ultrasound diagnostic apparatus (also referred to as an ultrasound probe) which is a kind of acoustic wave probe includes a piezoelectric element which transmits and receives an ultrasonic wave and an acoustic lens which is a portion coming into contact with a living body. An ultrasonic wave generated from the piezoelectric element is incident on the living body after being transmitted through the acoustic lens. In a case where the difference between acoustic impedance (density x acoustic velocity) of the acoustic lens and acoustic impedance of the living body is large, the ultrasonic wave is reflected by the surface of the living body. Therefore, the ultrasonic wave is not efficiently incident on the living body. For this reason, it is difficult to obtain a favorable resolution. In addition, it is desirable that ultrasonic attenuation of the acoustic lens is low in order to transmit and receive the ultrasonic wave with high sensitivity.

For this reason, a silicone resin of which the acoustic impedance is close to the acoustic impedance (in the case of a human body, <NUM> × <NUM><NUM> to <NUM> × <NUM><NUM> kg/m<NUM>/sec) of a living body and which has a low ultrasonic attenuation is used as a material of the acoustic lens.

For example, <CIT> discloses a composition for an ultrasound probe which contains at least three types of polyorganosiloxane mixtures containing specific branched polyorganosiloxane, and a silicone resin for an ultrasound probe obtained by vulcanizing the composition. In addition, <CIT> describes an ultrasound terminal obtained by vulcanizing and molding a composition in which silicone rubber having a dimethylpolysiloxane structure containing a vinyl group is filled with a specific amount of silica particles, with a vulcanizing agent.

A resin made of silicone is soft and has a low mechanical strength. For this reason, for the purpose of improving the hardness and the mechanical strength, mixing of an inorganic filler and/or a vinyl group-containing resin (also referred to as a reinforcing agent) is performed while increasing the molecular weight of a both-terminal vinyl silicone resin. However, in a case of intending to achieve the required mechanical strength, the amount of an inorganic filler and/or vinyl group-containing resin added to the silicone resin inevitably increases. For this reason, the viscosity of the composition before the vulcanizing becomes too high. Therefore, there are problems in that a special high-torque kneading machine becomes necessary or the acoustic attenuation increases.

Therefore, development of a resin composition which can be used for an acoustic wave probe has been an important challenge which has a viscosity required at the stage before vulcanizing and satisfies all of the high resin hardness, high tear strength, and reduction in acoustic attenuation at a high level after vulcanizing.

In view of the above-described circumstances, an object of the present invention is to provide a composition which can be used for an acoustic wave probe and which, before vulcanization, has a desired viscosity, and therefore, has excellent operability as kneading during production of a composition or molding and processing into an acoustic lens is easily performed and in which, after vulcanization, the acoustic impedance of the silicone resin is close to an acoustic impedance value of a living body, the acoustic attenuation is decreased, and the hardness and the tear strength can be improved.

In addition, another object of the present invention is to provide a silicone resin for an acoustic wave probe using the composition, the acoustic wave probe, an ultrasound probe, an acoustic wave measurement apparatus, an ultrasound diagnostic apparatus, a photoacoustic wave measurement apparatus, and an ultrasound endoscope.

Furthermore, still another object of the present invention is to provide a composition for an acoustic wave probe and a silicone resin for an acoustic wave probe which can improve the sensitivity of the ultrasound probe, in which capacitive micromachined ultrasonic transducers (cMUT) are used as ultrasonic diagnostic transducer arrays, the photoacoustic wave measurement apparatus, and the ultrasound endoscope by using the composition for an acoustic wave probe and the silicone resin for an acoustic wave probe as constituent materials of the ultrasound probe, the photoacoustic wave measurement apparatus, and the ultrasound endoscope.

The present inventors have conducted intensive studies. As a result, they have found that the above-described problems can be solved using a vulcanizable composition which contains specific polysiloxane including polysiloxane having a vinyl group and silica particles of which the average primary particle diameter is within a specific range and which are subjected to surface treatment, and have completed the present invention based on the findings.

To solve the he above-described problems the present invention provides the use of a composition comprising a polysiloxane mixture containing.

Also, the invention provides (i) a silicone resin for an acoustic wave probe which is obtained by vulcanizing the above composition and (ii) an acoustic wave probe comprising an acoustic lens and/or an acoustic matching layer, each made of this silicone resin and (iii).

Yet further, the invention provides an apparatus, which (iii) is selected from an ultrasound probe comprising a capacitive micromachined ultrasonic transducer as an ultrasonic transducer array, a photoacoustic wave measurement apparatus and ultrasound endoscope; and comprises an acoustic lens containing the present silicone resin, or (iv) is an acoustic wave measurement apparatus or an ultrasound diagnostic apparatus, and comprises the present acoustic wave probe.

Preferred embodiments of the present invention are as defined in the appended dependent claims and/or in the following detailed description.

Unless otherwise specified in the present description, in a case where there are groups having a plurality of the same reference numerals as each other in general formulae representing compounds, these may be the same as or different from each other, and a group (for example, an alkyl group) specified by each group may further have a substituent. In addition, the "Si-H group" means a group having three bonds on a silicon atom, but the description of the bonds is not repeated and the notation is simplified.

In addition, herein "to" means a range including numerical values denoted before and after "to" as a lower limit value and an upper limit value.

Unless otherwise specified, the mass average molecular weight (also referred to as Mw hereinafter) herein refers to a value (in terms of polystyrene) measured through gel permeation chromatography (GPC).

The above-described characteristics and advantages and other characteristics and advantages of the present invention become clearer in the following descriptions with reference to the accompanying drawing.

<FIG> is a perspective transparent view of an example of a convex ultrasound probe which is an embodiment of an acoustic wave probe.

A composition suitable for the present use for an acoustic wave probe (hereinafter, also simply referred to as the present composition) is a composition comprising a polysiloxane mixture containing.

The content of silica particles in <NUM> parts by mass (pbm) in total of the polysiloxane mixture is preferably <NUM>-<NUM> pbm, more preferably <NUM>-<NUM> pbm, and still more preferably <NUM>-<NUM> pbm. In a case where the content of the silica particles is within the above-described ranges, the tear strength, the bending durability, and the acoustic sensitivity increase.

In addition, the content of polysiloxane having a vinyl group in <NUM> pbm in total of the polysiloxane mixture is preferably <NUM>-<NUM> pbm. The content of polysiloxane having two or more Si-H groups in a molecular chain in <NUM> pbm in total of the polysiloxane mixture is preferably <NUM>-<NUM> pbm. The content of the polysiloxane having a vinyl group is more preferably <NUM>-<NUM> pbm and still more preferably <NUM>-<NUM> pbm. The content of the polysiloxane having two or more Si-H groups in a molecular chain is preferably <NUM>-<NUM> pbm, more preferably <NUM>-<NUM> pbm, still more preferably <NUM>-<NUM> pbm, and particularly preferably <NUM>-<NUM> pbm.

In a case where the content of the polysiloxane is within the above-described range, the hardness, the tear strength, and the acoustic impedance balance of the obtained vulcanized product (silicone resin) are excellent.

The polysiloxane mixture refers to a mixture which does not contain a catalyst for crosslinking and polymerizing (vulcanizing) the polysiloxane having a vinyl group and the polysiloxane having two or more Si-H groups in a molecular chain. Accordingly, the polysiloxane mixture contains silica particles but no catalyst.

In addition, <NUM> pbm in total of the polysiloxane mixture means that the total of the individual components contained in the polysiloxane mixture is <NUM> pbm.

Any of the above-described polysiloxanes contained in the polysiloxane mixture may be used as long as the polysiloxane has a vinyl group or two or more Si-H groups in a molecular chain. However, in the present invention, polyorganosiloxane (A) having a vinyl group and polyorganosiloxane (B) having two or more Si-H groups in a molecular chain are preferable.

Accordingly, in the present invention, a composition containing at least the polyorganosiloxane (A) having a vinyl group, the polyorganosiloxane (B) having two or more Si-H groups in a molecular chain, and silica particles (C) in a polyorganosiloxane mixture as components is preferable.

In the following detailed description, a polysiloxane mixture containing the polyorganosiloxane (A) having a vinyl group and the polyorganosiloxane (B) having two or more Si-H groups in a molecular chain will be described as a preferred embodiment. However, each polysiloxane contained in the polysiloxane mixture is not limited to the polyorganosiloxanes (A) and (B).

The polyorganosiloxane (A) having a vinyl group (hereinafter, also simply referred to as polyorganosiloxane (A)) used in the present invention preferably has two or more vinyl groups in a molecular chain.

Examples of the polyorganosiloxane (A) having a vinyl group include polyorganosiloxane (a) having vinyl groups at least at both terminals of a molecular chain (hereinafter, also simply referred to as polyorganosiloxane (a)) or polyorganosiloxane (b) having at least two -O-Si(CH<NUM>)<NUM>(CH=CH<NUM>) in a molecular chain (hereinafter, also simply referred to as polyorganosiloxane (b)). Among them, the polyorganosiloxane (a) having vinyl groups at least at both terminals of a molecular chain is preferable.

The polyorganosiloxane (a) is preferably linear and the polyorganosiloxane (b) is preferably polyorganosiloxane in which -O-Si(CH<NUM>)<NUM>(CH=CH<NUM>) is bonded to a Si atom constituting a main chain.

The polyorganosiloxane (A) having a vinyl group is subjected to hydrosilylation through a reaction with the polyorganosiloxane (B) having two or more Si-H groups in the presence of, for example, a platinum catalyst. A cross-linked (vulcanized) structure is formed through this hydrosilylation reaction (addition reaction).

The content of the vinyl group of the polyorganosiloxane (A) is not particularly limited. The content of the vinyl group is, for example, preferably <NUM>-<NUM> mol% and more preferably <NUM>-<NUM> mol% from the viewpoint of forming a sufficient network between components contained in a composition for an acoustic wave probe.

Here, the content of the vinyl group is represented by mol% of the vinyl group-containing siloxane unit based on <NUM> mol% of all the units constituting the polyorganosiloxane (A). One vinyl group-containing siloxane unit has <NUM>-<NUM> vinyl groups. Among them, one vinyl group is preferable for one vinyl group-containing siloxane unit. For example, in a case where all Si atoms of Si in a Si-O unit and at a terminal which constitute a main chain have at least one vinyl group, the content becomes <NUM> mol%.

In addition, the polyorganosiloxane (A) preferably has a phenyl group, and the content of the phenyl group of the polyorganosiloxane (A) is not particularly limited. The content of the phenyl group is, for example, preferably <NUM>-<NUM> mol% and preferably <NUM>-<NUM> mol% from the viewpoint of mechanical strength in a case where a silicone resin for an acoustic wave probe is made.

Here, the content of the phenyl group is represented by mol% of the phenyl group-containing siloxane unit based on <NUM> mol% of all the units constituting the polyorganosiloxane (A). One phenyl group-containing siloxane unit has <NUM>-<NUM> phenyl groups. Among them, two phenyl groups are preferable for one phenyl group-containing siloxane unit. For example, in a case where all Si atoms of Si in a Si-O unit and at a terminal which constitute a main chain have at least one phenyl group, the content becomes <NUM> mol%.

The "unit" refers to Si atoms in a Si-O unit and at a terminal which constitute a main chain.

The degree of polymerization and the specific gravity are not particularly limited. The degree of polymerization is preferably <NUM>-<NUM>,<NUM> and more preferably <NUM>-<NUM>,<NUM>, and the specific gravity is preferably <NUM>-<NUM> from the viewpoint of improving e.g. the mechanical strength, the hardness and the chemical stability of an obtained silicone resin for an acoustic wave probe (hereinafter, also simply referred to as a silicone resin).

The Mw of the polyorganosiloxane having a vinyl group is preferably <NUM>,<NUM>-<NUM>,<NUM>, more preferably <NUM>,<NUM>-<NUM>,<NUM>, and still more preferably <NUM>,<NUM>-<NUM>,<NUM> from the viewpoints of the mechanical strength, the hardness, and/or easiness of processing.

The Mw can be measured using, for example, TOLUENE (manufactured by Shonan Wako Junyaku K. ) as an eluent, TSKgel (registered trademark), G3000HXL + TSKgel (registered trademark), and G2000HXL as columns, and a RI detector under the conditions of a temperature of <NUM> and a flow rate of <NUM>/min after preparing a GPC apparatus HLC-<NUM> (manufactured by TOSOH CORPORATION).

The kinematic viscosity at <NUM> is preferably <NUM> × <NUM>-<NUM> to <NUM><NUM>/s, more preferably <NUM> × <NUM>-<NUM> to <NUM><NUM>/s, and still more preferably <NUM> × <NUM>-<NUM> to <NUM><NUM>/s.

The kinematic viscosity can be measured and obtained at a temperature of <NUM> using a Ubbelohde-type viscometer (for example, a trade name of SU manufactured by SIBATA SCIENTIFIC TECHNOLOGY LTD. ) in compliance with JIS Z8803.

Polyorganosiloxane of Formula (A) is preferable as the polyorganosiloxane (a) having vinyl groups at least at both terminals of a molecular chain.

In Formula (A), Ra1 is a vinyl group and each Ra2 and each Ra3 each independently are alkyl, cycloalkyl, alkenyl or aryl. x1 and x2 each independently are an integer of ≥ 1In addition, each of the groups of Ra2 and Ra3 may further have a substituent.

The number of carbon atoms in an alkyl group in Ra2 and Ra3 is preferably <NUM>-<NUM>, more preferably <NUM>-<NUM>, still more preferably <NUM> or <NUM>, and particularly preferably <NUM>. Examples of the alkyl group include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, n-hexyl, n-octyl, <NUM>-ethylhexyl and n-decyl.

The number of carbon atoms in a cycloalkyl group in Ra2 and Ra3 is preferably <NUM>-<NUM>, more preferably <NUM>-<NUM>, and still more preferably <NUM> or <NUM>. In addition, the cycloalkyl group is preferably a <NUM>-, <NUM>- or <NUM>-membered ring, and more preferably a <NUM>- or <NUM>-membered ring. Examples of the cycloalkyl group include cyclopropyl, cyclopentyl and cyclohexyl.

The number of carbon atoms in an alkenyl group in Ra2 and Ra3 is preferably <NUM>-<NUM>, more preferably <NUM>-<NUM>, and still more preferably <NUM>. Examples of the alkenyl group include vinyl, allyl and butenyl.

The number of carbon atoms in an aryl group in Ra2 and Ra3 is preferably <NUM>-<NUM>, more preferably <NUM>-<NUM>, and still more preferably <NUM>-<NUM>. Examples of the aryl group include phenyl, tolyl and naphthyl.

The alkyl, cycloalkyl, alkenyl and aryl group may have a substituent. Examples of such a substituent include halogen, alkyl, cycloalkyl, alkenyl, aryl, alkoxy, aryloxy, alkylthio, arylthio, silyl and cyano.

Examples of the group having a substituent include halogenated alkyl.

Ra2 and Ra3 are preferably alkyl, alkenyl or aryl, more preferably C<NUM>-<NUM>-alkyl, vinyl or phenyl, and still more preferably methyl, vinyl or phenyl.

Among them, Ra2 is preferably methyl. Ra3 is preferably methyl, vinyl or phenyl, more preferably methyl or phenyl, and particularly preferably phenyl. In addition, it is also preferable that both Ra2's in the repetition of x1 are phenyl groups.

x1 preferably is an integer of <NUM>-<NUM>,<NUM> more preferably of <NUM>-<NUM>,<NUM>.

x2 preferably is an integer of <NUM>-<NUM>,<NUM>, more preferably of <NUM>-<NUM>,<NUM>, still more preferably of <NUM>-<NUM>,<NUM>, and particularly preferably <NUM>-<NUM>.

In addition, as another embodiment, x1 preferably is an integer of <NUM>-<NUM>,<NUM> more preferably of <NUM>-<NUM>,<NUM>.

Examples of the polyorganosiloxane having vinyl groups at least at both terminals of a molecular chain include DMS series (for example, DMS-V31, DMS-V31S15, DMS-V33, DMS-V35, DMS-V35R, DMS-V41, DMS-V42, DMS-V46, DMS-V51, and DMS-V52), and PDV series (for example, PDV-<NUM>, PDV-<NUM>, PDV-<NUM>, PDV-<NUM>, PDV-<NUM>, PDV-<NUM>, PDV-<NUM>, and PDV-<NUM>), PMV-<NUM>, PVV-<NUM>, FMV-<NUM>, and EDV-<NUM> all of which are trade names manufactured by GELEST, INC.

In the DMS-V31S15, fumed silica is formulated into DMS-V31S15 in advance, and therefore, kneading using a special device is unnecessary.

The polyorganosiloxane (A) having a vinyl group may be used singly or in a combination of two or more thereof.

The polyorganosiloxane (B) having two or more Si-H groups in a molecular chain used in the present invention (hereinafter, also simply referred to as polyorganosiloxane (B)) has two or more Si-H groups in a molecular chain.

In a case where there are two or more Si-H groups in a molecular chain, it is possible to crosslink polyorganosiloxane having at least two polymerizable unsaturated groups.

There is a linear structure and a branched structure in the polyorganosiloxane (B), and the linear structure is preferable.

The Mw of a linear structure is preferably <NUM>-<NUM>,<NUM> and more preferably <NUM>,<NUM>-<NUM>,<NUM> from the viewpoints of the mechanical strength and the hardness.

The polyorganosiloxane (B) which has a linear structure and two or more Si-H groups in a molecular chain is preferably polyorganosiloxane of Formula (B).

In Formula (B), each individual Rb1-Rb3 each independently is H, alkyl, cycloalkyl, alkenyl, aryl or -O-Si(Rb5)<NUM>(Rb4). Each individual Rb4 and Rb5 independently is H, alkyl, cycloalkyl, alkenyl or aryl. y1 and y2 each independently are an integer of ≥ <NUM>. In addition, each of the groups of Rb1-Rb5 may further be substituted with a substituent. However, there are two or more Si-H groups in a molecular chain.

Alkyl, cycloalkyl, alkenyl and aryl in Rb1-Rb3 are synonymous with alkyl, cycloalkyl, alkenyl and aryl in Ra2 and Ra3, and preferred ranges thereof are also the same as each other.

Alkyl, cycloalkyl, alkenyl and aryl in Rb4 and Rb5 of -O-Si(Rb5)<NUM>(Rb4) are synonymous with alkyl, cycloalkyl, alkenyl and aryl in Rb1-Rb3, and preferred ranges thereof are also the same as each other.

Rb1-Rb3 are preferably H, alkyl, alkenyl, aryl or -O-Si(Rb5)<NUM>(Rb4), and more preferably H, C<NUM>-<NUM>-alkyl, vinyl, phenyl or -O-Si (CH<NUM>)<NUM>H.

Among them, Rb1 and Rb2 are preferably H, alkyl, alkenyl or aryl, more preferably H or alkyl, and still more preferably H or methyl.

Rb3 is preferably H, alkyl, alkenyl, aryl or -O-Si(Rb5)<NUM>(Rb4), more preferably H or aryl, and still more preferably H or phenyl.

In the present invention, in a case where Rb3 is phenyl, it is preferable that Rb1 is H. It is more preferable that Rb1 is H and the following conditions are satisfied.

In the above-described <NUM>), a case where Rb4 is H and Rb5 is alkyl is particularly preferable.

y1 preferably is an integer of <NUM>-<NUM>,<NUM>, more preferably of <NUM>-<NUM>,<NUM>, and still more preferably of <NUM>-<NUM>.

y2 preferably is an integer of <NUM>-<NUM>,<NUM>, more preferably of <NUM>-<NUM>,<NUM>, and still more preferably of <NUM>-<NUM>.

(y1+y2) preferably is an integer of <NUM>-<NUM>,<NUM>, more preferably of <NUM>-<NUM>,<NUM>, still more preferably of <NUM>-<NUM>, and particularly preferably of <NUM>-<NUM>.

As a combination of Rb1-Rb3, a combination of H or C<NUM>-<NUM>-alkyl as Rb1, C<NUM>-<NUM>-alkyl as Rb<NUM>, and H as Rb3 is preferable and a combination of C<NUM>-<NUM>-alkyl as Rb1, C<NUM>-<NUM>-alkyl as Rb2, and H as Rb3 is more preferable.

In the preferred combinations, the content of a hydrosilyl group represented by y2/(y1+y2) is preferably > <NUM> to <NUM> and more preferably > <NUM> to <NUM>.

Examples of the polyorganosiloxane (B) with a linear structure include HMS-<NUM> (MeHSiO: <NUM>-<NUM> mol%), HMS-<NUM> (MeHSiO: <NUM>-<NUM> mol%), HMS-<NUM> (MeHSiO: <NUM>-<NUM> mol%), and HMS-<NUM> (MeHSiO: <NUM>-<NUM> mol%) as methylhydrosiloxane-dimethylsiloxane copolymers (trimethylsiloxane terminated), HPM-<NUM> (MeHSiO: <NUM>-<NUM> mol%) as a methylhydrosiloxane-phenylmethylsiloxane copolymer, and HMS-<NUM> (MeHSiO: <NUM> mol%) as a methylhydrosiloxane polymer, all of which are trade names of GELEST, INC.

Here, the mol% of MeHSiO has the same meaning as that y2/(y1+y2) in the above-described preferred combination of Rb1-Rb3 is multiplied by <NUM>.

It is preferable that both the linear structure and the branched structure have no vinyl group from the viewpoint of preventing the progress of a cross-linking reaction within a molecule. Among these, it is preferable that the branched structure has no vinyl group.

The polyorganosiloxane (B), which has a branched structure and two or more Si-H groups in a molecular chain, has a branched structure and two or more hydrosilyl groups (Si-H groups).

The specific gravity is preferably <NUM>-<NUM>.

The polyorganosiloxane (B) with a branched structure is preferably represented by Average Composition Formula [Ha(Rb6)<NUM>-aSiO<NUM>/<NUM>]y3[SiO<NUM>/<NUM>]y4 (b), wherein Rb6 is alkyl, cycloalkyl, alkenyl or aryl, a is <NUM>-<NUM>, and y3 and y4 each independently are an integer of ≥ <NUM>.

Alkyl, cycloalkyl, alkenyl and aryl in Rb6 are synonymous with alkyl, cycloalkyl, alkenyl and aryl in Ra2 and Ra3, and preferred ranges thereof are also the same as each other. a is preferably <NUM>.

The content of a hydrosilyl group represented by a/<NUM> is preferably > <NUM> and < <NUM> and more preferably > <NUM> and < <NUM>.

In contrast, in a case of representing the polyorganosiloxane (B) with a branched structure using a chemical structural formula, polyorganosiloxane in which -O-Si(CH<NUM>)<NUM>(H) is bonded to a Si atom constituting a main chain is preferable and polyorganosiloxane having a structure of Formula (Bb) is more preferable.

In Formula (Bb), * means a bond with at least a Si atom of siloxane.

Examples of the polyorganosiloxane (B) with a branched structure include HQM-<NUM> (trade name of Hydride Q Resin manufactured by GELEST, INC. ) and HDP-<NUM> (trade name of polyphenyl-(dimethylhydroxy)siloxane (hydride terminated),[(HMe<NUM>SiO)(C<NUM>H<NUM>Si)O]: <NUM>-<NUM> mol% manufactured by GELEST, INC.

The polyorganosiloxane (B) having two or more Si-H groups in a molecular chain used in the present invention may be used singly, or in a combination of two or more thereof. In addition, the polyorganosiloxane (B) with a linear structure and the polyorganosiloxane (B) with a branched structure may be used in combination.

The silica particles (C) used in the present invention are silica particles which have an average primary particle diameter of <NUM>-<NUM> and are subjected to surface treatment, and have a methanol hydrophobicity (MH) of <NUM>-<NUM> mass-%.

An effect of improving the acoustic impedance, the hardness, and the mechanical strength of a silicone resin is obtained by adding silica particles to the silicone resin. However, the acoustic attenuation increases with an increase in the amount of the silica particles added, and in a case where the addition amount is too large, the viscosity of the composition for an acoustic wave probe before vulcanizing increases.

However, it is considered that, in a case where the silica particles (C) subjected to surface treatment which have a particle diameter within a specific range are used, it is possible to reduce the acoustic attenuation and reduce the viscosity before vulcanizing. The reason for this is not yet certain, but it is presumed as follows.

That is, in a case where silica particles having a small average primary particle diameter are used, the tear strength of the silicone resin is improved and increase in the acoustic attenuation is suppressed, whereas the viscosity of the composition for an acoustic wave probe before vulcanizing increases. By subjecting surface treatment on silica particles having an average primary particle diameter within the above-described specific range, an interaction with polyorganosiloxane becomes stronger and the affinity increases. For this reason, it is considered that aggregation of silica particles having a small average primary particle diameter is suppressed, the viscosity of the composition for an acoustic wave probe before vulcanizing is suppressed, the tear strength of the silicone resin after vulcanizing is high, and the acoustic attenuation is decreased.

The average primary particle diameter of the silica particles (C) is <NUM>-<NUM>, preferably <NUM>-<NUM>, and still more preferably <NUM>-<NUM> from the viewpoints of suppressing increase in the viscosity of the composition for an acoustic wave probe before vulcanizing, suppressing increase in the acoustic attenuation of the silicone resin, and improving the tear strength.

Here, the average primary particle diameter means a volume average particle diameter. The volume average particle diameter can be obtained by, for example, measuring the particle diameter distribution using a laser diffraction scattering type particle diameter distribution measurement apparatus (for example, trade name "LA910" manufactured by HORIBA, Ltd. In the present specification, for silica particles of which the average primary particle diameter has not been disclosed in the catalog or for silica particles newly manufactured, the average primary particle diameter is obtained through the above-described measurement method.

Here, the average primary particle diameter of the silica particles (C) means an average primary particle diameter in a state in which the surface treatment has been performed.

The silica particles (C) may be used singly or in a combination of two or more thereof.

The specific surface area of the silica particles (C) is preferably <NUM>-<NUM><NUM>/g, more preferably <NUM>-<NUM><NUM>/g, and particularly preferably <NUM>-<NUM><NUM>/g from the viewpoint of improving the hardness and/or the mechanical strength of a silicone resin to be obtained.

The silica particles (C) are silica particles whose surface has been treated, and preferably silica particles subjected to surface treatment with a silane compound.

A usual technique may be used as a technique of the surface treatment. Examples of the technique of the surface treatment using a silane compound include a technique of performing surface treatment using a silane coupling agent and a technique of performing coating using a silicone compound.

A silane coupling agent having a hydrolyzable group is preferable as a silane coupling agent from the viewpoint of improving the hardness and/or the mechanical strength of a silicone resin. Surface modification of silica particles is performed such that a hydrolyzable group in a silane coupling agent becomes a hydroxyl group after being hydrolyzed using water and this hydroxyl group is subjected to a dehydration and condensation reaction with a hydroxyl group on the surfaces of the silica particles, thereby improving the hardness and/or the mechanical strength of an obtained silicone resin. Examples of the hydrolyzable group include an alkoxy group, an acyloxy group, and a halogen atom.

In a case where the surfaces of silica particles are hydrophobically modified, affinity between the silica particles (C) and the polyorganosiloxanes (A) and (B) becomes favorable, and therefore, the hardness and the mechanical strength of an obtained silicone resin are improved, which is preferable.

Examples of a silane coupling agent having a hydrophobic group as a functional group include alkoxysilanes such as methyltrimethoxysilane (MTMS), dimethyldimethoxysilane, phenyltrimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, hexyltrimethoxysilane, hexyl triethoxysilane, and decyltrimethoxysilane; chlorosilanes such as methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, and phenyltrichlorosilane; and hexamethyldisilazane (HMDS).

In addition, examples of a silane coupling agent having a vinyl group as a functional group include alkoxysilanes such as methacryloxypropyltriethoxysilane, methacryloxypropyltrimethoxysilane, methacryloxypropylmethyldiethoxysilane, methacryloxypropylmethyldimethoxysilane, vinyltriethoxysilane, vinyl trimethoxysilane, and vinylmethyldimethoxysilane; chlorosilanes such as vinyltrichlorosilane and vinylmethyldichlorosilane; and divinyltetramethyldisilazane.

Silica particles treated with a trialkylsilylating agent are preferable and silica particles treated with a trimethylsilylating agent are more preferable as the silica particles (C) subjected to surface treatment with a silane coupling agent.

Examples of the silane compound include the above-described silane coupling agents and a silane coupling agent in which a functional group in a silane coupling agent is substituted with an alkyl group.

In addition, examples of the trimethylsilylating agent include trimethylchlorosilane and hexamethyldisilazane (HMDS) described in the above-described silane coupling agent, and methyltrimethoxysilane (MTMS) and trimethylmethoxysilane which are silane coupling agents in which a functional group is substituted with an alkyl group.

Examples of a commercially available silane coupling agent include hexamethyldisilazane (HMDS) (trade name: HEXAMETHYLDISILAZANE (SIH6110. <NUM>) manufactured by GELEST, INC.

A hydroxyl group existing on the surfaces of silica particles is covered with a trimethylsilyl group through a reaction with e.g. hexamethyldisilazane (HMDS), methyltrimethoxysilane (MTMS) and trimethylmethoxysilane, and the surfaces of the silica particles are hydrophobically modified.

In the present invention, the silane coupling agent may be used alone or in a combination of two or more thereof.

A silicone compound with which the silica particles (C) are coated may be a polymer formed through siloxane bonding.

Examples of the silicone compound include a silicone compound in which all or a part of side chains and/or terminals of polysiloxane has become methyl, a silicone compound in which a part of a side chain is H, a modified silicone compound in which organic groups such as amino and/or epoxy is introduced into all or a part of side chains and/or terminals, and a silicone resin having a branched structure. The silicone compound may be either of a linear structure or a cyclic structure.

Examples of the silicone compound in which all or a part of side chains and/or terminals of polysiloxane has become methyl include monomethylpolysiloxane such as polymethylhydrosiloxane (hydride terminated), polymethylhydrosiloxane (trimethylsiloxy terminated), polymethylphenylsiloxane (hydride terminated), and polymethylphenylsiloxane (trimethylsiloxy terminated); and dimethylpolysiloxanes such as dimethylpolysiloxane (hydride terminated), dimethylpolysiloxane (trimethylsiloxy terminated), and cyclic dimethylpolysiloxane.

Examples of the silicone compound in which a part of side chains is H include methylhydrosiloxane-dimethylsiloxane copolymer (trimethylsiloxy terminated), methylhydrosiloxane-dimethylsiloxane copolymer (hydride terminated), polymethylhydrosiloxane (hydride terminated), polymethylhydrosiloxane (trimethylsiloxy terminated), polyethylhydrosiloxane (triethylsiloxy terminated), polyphenyl-(dimethylhydrosiloxy) siloxane (hydride terminated), methylhydrosiloxane-phenylmethylsiloxane copolymer (hydride terminated), methylhydrosiloxane-octylmethylsiloxane copolymer, and methylhydrosiloxane-octylmethylsiloxane-dimethylsiloxane terpolymer.

In addition, examples of modified silicone into which an organic group is introduced include reactive silicone into which amino, epoxy, methoxy, (meth)acryloyl, a phenol group, a carboxylic anhydride group, hydroxy, mercapto, carboxyl, and/or an organic group of a hydrogen atom are introduced; and non-reactive silicone modified with polyether, aralkyl, fluoroalkyl, long chain alkyl, long chain aralkyl, higher fatty acid ester, higher fatty acid amide, and/or polyether methoxy.

Silica particles coated with a silicone compound can be obtained through a usual method. For example, the silica particles can be obtained by being mixed and stirred in dimethylpolysiloxane for a certain period of time and being filtered.

In addition, in a case of using reactive modified silicone as a silicone compound, surface modification of silica particles is performed through reaction of an organic group with a hydroxyl group of the surfaces of the silica particles, and therefore, the hardness and/or the mechanical strength of an obtained silicone resin is improved.

An Example of the commercially available silicone compound includes methyl hydrogen silicone oil (MHS) (trade name: KF-<NUM>, manufactured by Shin-Etsu Chemical Co. ) which is polymethylhydrosiloxane (trimethylsiloxy terminated).

The methanol hydrophobicity of the silica particles (C) which is calculated through the following methanol titration test is <NUM>-<NUM> mass%, preferably <NUM>-<NUM> mass%, and more preferably <NUM>-<NUM> mass%. Here, the larger the methanol hydrophobicity, the higher the hydrophobicity, and the smaller the methanol hydrophobicity, the higher the hydrophilicity.

<NUM> of ion exchange water and <NUM> of silica particles as samples are placed in a beaker at <NUM> and stirred with a magnetic stirrer, methanol is added dropwise thereto from a burette, and the amount (Xg) of methanol added dropwise until the whole sample settles is measured. The methanol hydrophobicity is calculated using the following equation.

In a case where the methanol hydrophobicity is within the above-described preferred ranges, it is possible to suppress decrease in acoustic sensitivity in a case where a silicone resin for an acoustic wave probe is obtained without increase in the viscosity of the composition for an acoustic wave probe before vulcanizing.

The Wardell's sphericity of a primary particle of the silica particles (C) is preferably <NUM>-<NUM>, more preferably <NUM>-<NUM>, and still more preferably <NUM>-<NUM>.

Here, the "Wardell's sphericity" (refer to <NPL>) is an index obtained by measuring the sphericity of a particle as(diameter of circle equal to projection area of particle) / (diameter of minimum circle circumscribing projection image of particle). A particle having the index closer to <NUM> means a particle closer to a true sphere.

It is possible to use, for example, a scanning electron microscope (SEM) photograph can be used to measure the Wardell's sphericity (hereinafter, also simply referred to as sphericity). Specifically, for example, about <NUM> primary particles are observed using the SEM photograph, and each sphericity thereof is calculated. An average value obtained by dividing the total of the calculated sphericities by the number of observed primary particles is regarded as the sphericity.

In a case where the Wardell's sphericity is within the above-described preferred ranges, it is considered that the acoustic sensitivity is improved because the area of the acoustic wave hitting the silica particles becomes smaller in a case where the silicone resin is irradiated with the acoustic wave. In particular, it is considered that the acoustic sensitivity is more effectively improved in a case where the shapes of the silica particles (C) are truly spherical within a specific range of the average primary particle diameter of the silica particle (C) of the present invention.

In this specification, the "true spherical shape" also includes a slightly distorted sphere of which the Wardell's sphericity is within a range of <NUM>-<NUM>.

The silica particles are roughly classified into combustion method silica (that is, fumed silica) obtained by burning a silane compound, deflagration method silica obtained by explosively burning metallic silicon powder, wet-type silica (among which silica synthesized under alkaline conditions is referred to as precipitation method silica and silica synthesized under acidic conditions is referred to as gel method silica) obtained through a neutralization reaction with sodium silicate and mineral acid, and sol-gel method silica (so-called Stoeber method) obtained through hydrolysis of hydrocarbyloxysilane depending on its production method.

Preferred examples of a method for producing truly spherical silica particles include an explosion method and a sol-gel method.

The sol-gel method is a method of obtaining hydrophilic spherical silica particles essentially consisting of SiO<NUM> units by hydrolyzing and condensing a hydrocarbyloxysilane (preferably tetrahydrocarbyloxysilane) or a partial hydrolytic condensation product thereof or a combination thereof.

In addition, the hydrophobic treatment of the surfaces of the silica particles can also be carried out by introducing R<NUM><NUM>SiO<NUM>/<NUM> units (R<NUM> each independently is an optionally substituted monovalent C<NUM>-<NUM>-hydrocarbon group) onto the surfaces of hydrophilic spherical silica particles.

Specifically, the hydrophobic treatment thereof can be carried out, for example, through methods disclosed in <CIT> and <CIT>.

In general, the vinyl group possessed by the polyorganosiloxane (A) and the Si-H group possessed by the polyorganosiloxane (B) stoichiometrically react with each other in a ratio of <NUM>:<NUM>.

However, the equivalent of the Si-H group possessed by the polyorganosiloxane (B) to the vinyl group possessed by the polyorganosiloxane (A) from the viewpoint of a reaction between all the vinyl groups with the Si-H groups is preferably vinyl group : Si-H group = <NUM>:<NUM>-<NUM>:<NUM> and more preferably <NUM>:<NUM>-<NUM>:<NUM>.

In the composition for an acoustic wave probe, it is possible to appropriately formulate a platinum catalyst for an addition polymerization reaction, a vulcanization retardant, a solvent, a dispersant, a pigment, a dye, an antistatic agent, an antioxidant, a flame retardant, and/or a thermal conductivity enhancer in addition to the polyorganosiloxane (A) having a vinyl group, the polyorganosiloxane (B) having two or more Si-H groups in a molecular chain, and the silica particles (C).

Examples of the catalyst include platinum or a platinum-containing compound (hereinafter, also simply referred to as a platinum compound). Any platinum or platinum compound can be used.

Specific examples thereof include a catalyst in which platinum black or platinum is carried on e.g. an inorganic compound or carbon black; platinum chloride or an alcohol solution of platinum chloride; a complex salt of platinum chloride and olefin; and a complex salt of platinum chloride and vinyl siloxane. The catalyst may be used singly, or in a combination of two or more thereof.

The catalyst is necessary in the hydrosilylation reaction in which the Si-H group of the polyorganosiloxane (B) is added to the vinyl group of the polyorganosiloxane (A). The polyorganosiloxane (A) is cross-linked by the polyorganosiloxane (B) due to progress of a hydrosilylation reaction (addition vulcanization reaction) to form a silicone resin.

Here, the catalyst may be contained in the composition for an acoustic wave probe of the present invention or may be brought into contact with the composition for an acoustic wave probe without being contained in the composition for an acoustic wave probe. The latter case is preferable.

Examples of commercially available platinum catalyst include platinum compounds (a trade name of PLATINUM CYCLOVINYLMETHYLSILOXANE COMPLEX IN CYCLIC METHYLVINYLSILOXANES (SIP6832. <NUM>) with <NUM> mass% of Pt concentration; and a trade name of PLATINUM DIVINYLTETRAMETHYLDISILOXANE COMPLEX IN VINYL-TERMINATED POLYDIMETHYLSILOXANE (SIP6830. <NUM>) with <NUM> mass% of Pt concentration, all of which are manufactured by GELEST, INC.

In a case where a catalyst is contained in the composition for an acoustic wave probe of the present invention, the content of the catalyst present with respect to <NUM> pbm of a polysiloxane mixture is not particularly limited, but is preferably <NUM>-<NUM> pbm, more preferably <NUM>-<NUM> pbm, still more preferably <NUM>-<NUM> pbm, and particularly preferably <NUM>-<NUM> pbm from the viewpoint of reactivity.

In addition, it is possible to control the vulcanization temperature by selecting an appropriate platinum catalyst. For example, platinum-vinyldisiloxane is used for room temperature vulcanization (RTV) at ≤ <NUM> and platinum-cyclic vinylsiloxane is used for high temperature vulcanization (HTV) at ≥ <NUM>.

In the present invention, a vulcanization retardant for vulcanization reaction can be appropriately used. The vulcanization retardant is used for delaying the above-described addition vulcanization reaction and examples thereof include a low molecular weight vinylmethylsiloxane homopolymer (trade name: VMS-<NUM> manufactured by GELEST, INC.

The vulcanization rate, that is, the working time can be adjusted depending on the content of the vulcanization retardant.

The viscosity of the composition for an acoustic wave probe before performing a vulcanization reaction is preferably low. In a case where the viscosity is too high, it becomes difficult to prepare a composition for an acoustic wave probe in which the silica particles (C) are dispersed through kneading. The viscosity of the composition for an acoustic wave probe before adding a catalyst which initiates the vulcanization reaction is measured to measure the viscosity before vulcanizing. Specifically, the viscosity can be measured using a viscosity/viscoelasticity measurement apparatus (for example, trade name "RheoStress RS6000" manufactured by HAAKE) under the conditions of a temperature of <NUM> and a shear rate of <NUM>-<NUM>.

The viscosity (at <NUM>) measured under the above-described conditions is preferably ≤ <NUM>,<NUM> Pa·s, more preferably ≤ <NUM>,<NUM> Pa·s, and particularly preferably ≤ <NUM> Pa·s. The realistic lower limit value is ≥ <NUM> Pa·s.

In a case where the viscosity is within the above-described preferred ranges, the composition for an acoustic wave probe can be easily handled during processing. In addition, since residual air bubbles in the composition for an acoustic wave probe can be suppressed, an increase in acoustic attenuation caused by air bubbles in the silicone resin for an acoustic wave probe can also be suppressed.

The composition for an acoustic wave probe can be produced through any method.

For example, the composition for an acoustic wave probe can be obtained by kneading components constituting the composition for an acoustic wave probe using a kneader, a pressure kneader, a Banbury mixer (continuous kneader), and a kneading device with two rolls. The order of mixing the components is not particularly limited.

It is preferable to first make a polyorganosiloxane mixture in which the silica particles (C) are dispersed in the polyorganosiloxane (A) having a vinyl group and the polyorganosiloxane (B) having two or more Si-H groups in a molecular chain, from the viewpoint of obtaining a homogeneous composition. Thereafter, it is possible to produce a composition for an acoustic wave probe after adding a catalyst to the polyorganosiloxane mixture, in which the silica particles (C) are dispersed, and performing defoamation under reduced pressure.

The kneading conditions of the polyorganosiloxane mixture in which the silica particles (C) are dispersed are not particularly limited as long as the silica particles (C) are dispersed. For example, the polyorganosiloxane mixture is preferably kneaded at <NUM>-<NUM> for <NUM>-<NUM> hours.

It is possible to obtain a silicone resin for an acoustic wave probe of the present invention by vulcanizing the composition for an acoustic wave probe of the present invention which has been obtained in this manner. Specifically, it is possible to obtain a silicone resin for an acoustic wave probe by, for example, thermally vulcanizing the composition for an acoustic wave probe for <NUM>-<NUM> minutes at <NUM>-<NUM>.

The present silicone resin is obtained by vulcanizing the present composition. That is, the polyorganosiloxane (A) in the present composition is cross-linked with the polyorganosiloxane (B) through the above-described addition vulcanization reaction.

Hereinafter, the mechanical strength and the acoustic characteristics of a silicone resin will be described in detail.

Here, ultrasonic characteristics among the acoustic characteristics will be described. However, the acoustic characteristics are not limited to the ultrasonic characteristics, and relates to acoustic characteristics at an appropriate frequency which is selected in accordance with e.g. a test object and measurement conditions.

The type A durometer hardness of a silicone resin sheet with a thickness of <NUM> is measured using a rubber hardness meter (for example, trade name "RH-201A" manufactured by Excel co. ) in compliance with JIS K6253-<NUM> (<NUM>).

The hardness is preferably ≥ <NUM>, more preferably ≥ <NUM>, and still more preferably ≥ <NUM> from the viewpoint of preventing deformation in a case where the silicone resin sheet is incorporated into an acoustic wave probe as a part of the acoustic wave probe. A practical upper limit value is ≤ <NUM>.

A trouser-type test piece of a silicone resin sheet with a thickness of <NUM> is manufactured and the tear strength is measured in compliance with JIS K6252 (<NUM>).

The tear strength is preferably ≥ <NUM> N/cm and more preferably ≥ <NUM> N/cm. A practical upper limit value is ≤ <NUM> N/cm.

The density of a silicone resin sheet with a thickness of <NUM> at <NUM> is measured using an electronic gravimeter (for example, a trade name of "SD-<NUM>" manufactured by ALFA MIRAGE) in accordance with a density measurement method of a method A (underwater substitution method) disclosed in JIS K7112 (<NUM>). The acoustic velocity of an acoustic wave is measured at <NUM> using a sing-around type acoustic velocity measurement apparatus (for example, a trade name of "UVM-<NUM> type" manufactured by Ultrasonic Engineering Co. ) in compliance with JIS Z2353 (<NUM>) and acoustic impedance is obtained from a sum of the density and the acoustic velocity which had been measured.

A sinusoidal signal (a wave) of <NUM> which had been output from an ultrasound oscillator (for example, a function generator with a trade name of "FG-<NUM>" manufactured by IWATSU ELECTRIC CO. ) is input into an ultrasound probe (for example, manufactured by JAPAN PROBE), and an ultrasound pulse wave with a center frequency of <NUM> is generated in water from the ultrasound probe. The magnitude of the amplitude before and after the generated ultrasonic wave passed through a silicone resin sheet with a thickness of <NUM> is measured in a water temperature environment of <NUM> using an ultrasound receiver (for example, an oscilloscope with a trade name of "VP-5204A" manufactured by Matsushita Electric Industrial Co. ) The acoustic (ultrasonic) attenuations of each sheet are compared with each other by comparing the acoustic (ultrasonic) sensitivities of each sheet with each other.

The acoustic (ultrasonic) sensitivity is a numerical value given by the following calculation equation.

In the following calculation equation, Vin represents a voltage peak value of an input wave which is generated by the ultrasound oscillator and has a half-width of ≤ <NUM> nsec. Vs represents a voltage value obtained when the ultrasound oscillator receives an acoustic wave (ultrasonic wave) that the acoustic wave (ultrasonic wave) generated passes through a sheet and is reflected from an opposite side of the sheet.

In an evaluation system in the present invention, the acoustic (ultrasonic) sensitivity is preferably greater than or equal to -<NUM> dB.

The present composition is useful for medical members and can preferably be used, for example, in an acoustic wave probe or an acoustic wave measurement apparatus. The present acoustic wave measurement apparatus is not limited to an ultrasound diagnostic apparatus or a photoacoustic wave measurement apparatus, and is referred to as an apparatus that receives an acoustic wave which has been reflected or generated from an object and displays the received acoustic wave as an image or a signal strength.

Particularly, the present composition can suitably be used in: a material of an acoustic matching layer which is provided in an acoustic lens of an ultrasound diagnostic apparatus or between a piezoelectric element and the acoustic lens and plays a role of matching acoustic impedance between the piezoelectric element and the acoustic lens; a material of an acoustic lens in a photoacoustic wave measurement apparatus or an ultrasound endoscope; and a material of an acoustic lens in an ultrasound probe including capacitive micromachined ultrasonic transducers (cMUT) as an ultrasonic transducer array.

Specifically, the present silicone resin is preferably applied to, for example, an ultrasound diagnostic apparatus disclosed in <CIT> and <CIT> or an acoustic wave measurement apparatus such as a photoacoustic wave measurement apparatus disclosed in e.g. <CIT>, <CIT>, <CIT>, <CIT> or <CIT>.

A configuration of an acoustic wave probe of the present invention will be described below in more detail based on a configuration of an ultrasound probe in an ultrasound diagnostic apparatus which is described in <FIG>. The ultrasound probe is a probe which particularly uses an ultrasonic wave as an acoustic wave in an acoustic wave probe. For this reason, a basic configuration of the ultrasound probe can be applied to the acoustic wave probe as it is.

An ultrasound probe <NUM> is a main component of the ultrasound diagnostic apparatus and has a function of generating an ultrasonic wave and transmitting and receiving an ultrasonic beam. The configuration of the ultrasound probe <NUM> is provided in the order of an acoustic lens <NUM>, an acoustic matching layer <NUM>, a piezoelectric element layer <NUM>, and a backing material <NUM> from a distal end (the surface coming into contact with a living body which is a test object) as shown in <FIG>. In recent years, an ultrasound probe having a laminated structure in which an ultrasonic transducer (piezoelectric element) for transmission and an ultrasonic transducer (piezoelectric element) for reception are formed of materials different from each other has been proposed in order to receive high-order harmonics.

The piezoelectric element layer <NUM> is a portion which generates an ultrasonic wave and in which an electrode is attached to both sides of a piezoelectric element. In a case where voltage is applied to the electrode, the piezoelectric element layer generates an ultrasonic wave through repeated contraction and expansion of the piezoelectric element and through vibration.

Inorganic piezoelectric bodies of so-called ceramics obtained by e.g. polarizing crystals, single crystals such as LiNbO<NUM>, LiTaO<NUM>, and KNbO<NUM>, thin films of ZnO and AlN, and Pb(Zr,Ti)O<NUM>-based sintered body are widely used as the material constituting a piezoelectric element. In general, piezoelectric ceramics such as lead zirconate titanate (PZT) with good conversion efficiency are used.

In addition, sensitivity having a wider band width is required for a piezoelectric element detecting a reception wave on a high frequency side. For this reason, an organic piezoelectric body has been used in which an organic polymer material such as polyvinylidene fluoride (PVDF) is used as the piezoelectric element being suitable for a high frequency or a wide band.

Furthermore, cMUT using micro electro mechanical systems (MEMS) technology in which an array structure, which shows excellent short pulse characteristics, excellent broadband characteristics, and excellent mass productivity and has less characteristic variations, is obtained is disclosed in e.g. <CIT>.

In the present invention, it is possible to preferably use any piezoelectric element material.

The backing material <NUM> is provided on a rear surface of the piezoelectric element layer <NUM> and contributes to the improvement in distance resolution in an ultrasonic diagnostic image by shortening the pulse width of an ultrasonic wave through the suppression of excess vibration.

The acoustic matching layer <NUM> is provided in order to reduce the difference in acoustic impedance between the piezoelectric element layer <NUM> and a test object and to efficiently transmit and receive an ultrasonic wave.

The present composition can preferably be used as a material for the acoustic matching layer since the difference in acoustic impedance (<NUM> × <NUM><NUM> to <NUM> × <NUM><NUM> kg/m<NUM>/sec) between the piezoelectric element layer and a living body is small. The acoustic matching layer preferably contains ≥ <NUM> mass% of the present silicone resin obtained by subjecting the present composition to a vulcanization reaction.

The acoustic lens <NUM> is provided to improve resolution by making an ultrasonic wave converge in a slice direction using refraction. In addition, it is necessary for the acoustic lens to achieve matching of an ultrasonic wave with acoustic impedance (<NUM> × <NUM><NUM> to <NUM> × <NUM><NUM> kg/m<NUM>/sec in a case of a human body) of a living body which is a test object after being closely attached to the living body and to reduce ultrasonic attenuation of the acoustic lens <NUM> itself.

That is, sensitivity of transmission and reception of an ultrasonic wave is improved using a material of which the acoustic velocity is sufficiently lower than that of a human body, the ultrasound attenuation is low, and the acoustic impedance is close to a value of the skin of a human body, as the material of the acoustic lens <NUM>.

The present composition as a composition for the present ultrasound probe can also preferably be used as a material of the acoustic lens.

The operation of the ultrasound probe <NUM> having such a configuration will be described. The piezoelectric element layer <NUM> is resonated after applying voltage to the electrodes provided on both sides of a piezoelectric element, and an ultrasound signal is transmitted to a test object from the acoustic lens. During reception of the ultrasonic signal, the piezoelectric element layer <NUM> is vibrated using the signal (echo signal) reflected from the test object and this vibration is electrically converted into a signal to obtain an image.

Particularly, a remarkable effect of improving the sensitivity can be checked from a transmission frequency of an ultrasonic wave of ≥ <NUM> using the acoustic lens obtained from the composition for an ultrasound probe of the present invention as a general medical ultrasonic transducer. Particularly, a remarkable effect of improving the sensitivity can particularly be expected from a transmission frequency of an ultrasonic wave of ≥ <NUM>.

Hereinafter, an apparatus in which the acoustic lens obtained from the present composition for an ultrasound probe exhibits a function particularly regarding conventional problems will be described in detail.

The present composition exhibits an excellent effect even with respect to other apparatuses disclosed below.

In a case where cMUT apparatuses disclosed in e.g. <CIT>, and <CIT> are used in an ultrasonic diagnostic transducer array, the sensitivity thereof generally becomes low compared to a transducer in which usual piezoelectric ceramics (PZT) is used.

However, it is possible to make up for deficient sensitivity of cMUT using the acoustic lens obtained from the present composition. Accordingly, it is possible to make the sensitivity of cMUT to performance of a conventional transducer.

The cMUT apparatus is manufactured through MEMS technology. Therefore, it is possible to provide an inexpensive ultrasound probe, of which mass productivity is higher than that of a piezoelectric ceramics probe, to the market.

Photoacoustic imaging (photo acoustic imaging: PAI) disclosed in e.g. <CIT> displays a signal strength of an ultrasonic wave or an image obtained by imaging the ultrasonic wave generated in a case where human tissue is adiabatically expanded using light (magnetic wave) with which the interior of a human body is irradiated.

Here, the amount of an acoustic pressure of an ultrasonic wave generated through light irradiation is minute, and therefore, there is a problem in that it is difficult to observe deeper regions of a human body.

However, it is possible to exhibit an effect effective for the problem using the acoustic lens obtained from the present composition.

In an ultrasonic wave in an ultrasound endoscope disclosed in e.g. <CIT>, a signal line cable is structurally long compared to that of a transducer for a body surface, and therefore, there is a problem of improving the sensitivity of the transducer accompanied by loss of the cable. Regarding this problem, it is said that there are no effective means for improving the sensitivity due to the following reasons.

First, in a case of an ultrasound diagnostic apparatus for a body surface, it is possible to install e.g. an amplifier circuit or an AD conversion IC at a distal end of the transducer. In contrast, the ultrasound endoscope is inserted into a body. Therefore, there is a small installation space within the transducer, and thus, it is difficult to install the amplifier circuit or the AD conversion IC at a distal end of the transducer.

Secondly, it is difficult to apply a piezoelectric single crystal employed in the transducer in the ultrasound diagnostic apparatus for a body surface onto a transducer with an ultrasonic transmission frequency of ≥ <NUM> to <NUM> due to physical properties and processing suitability. However, an ultrasonic wave for an endoscope is generally a probe having an ultrasonic transmission frequency ≥ <NUM> to <NUM>, and therefore, it is also difficult to improve the sensitivity using piezoelectric single crystal material.

However, it is possible to improve the sensitivity of the ultrasonic transducer for an endoscope using the acoustic lens obtained from the present composition.

In addition, even in a case of using the same ultrasonic transmission frequency (for example, <NUM>), the efficacy is particularly exhibited in a case of using the acoustic lens obtained from the present composition in the ultrasonic transducer for an endoscope.

The present invention will be described in more detail based on Examples in which an ultrasonic wave is used as an acoustic wave. The present invention is not limited to the ultrasonic wave, and any acoustic wave of an audible frequency may be used as long as an appropriate frequency is selected in accordance with e.g. a test object and measurement conditions.

<NUM> pbm of a vinyl terminated diphenylsiloxane-dimethylsiloxane copolymer ("PDV-<NUM>" manufactured by GELEST, INC. with a Mw of <NUM>,<NUM> and a diphenylsiloxane amount of <NUM> mol%), <NUM> pbm of polymethylhydrosiloxane ("HMS-<NUM>" manufactured by GELEST, INC. with a Mw of <NUM>,<NUM>), and <NUM> pbm of truly spherical surface-treated silica ("QSG-<NUM>" manufactured by Shin-Etsu Chemical Co. with an average primary particle diameter of <NUM> which was a surface-treated product with methyltrimethoxysilane and hexamethyldisilazane (HMDS) and had a methanol hydrophobicity degree of <NUM> mass%) were kneaded with a kneader for <NUM> hours at a set temperature of <NUM> to obtain a homogeneous paste. <NUM> parts by weight of a platinum catalyst solution (manufactured by GELEST, INC. , trade name of "SIP6830. <NUM>" with <NUM> mass% of Pt concentration) was added to and mixed with the paste. Then, the mixture was subjected to defoaming under reduced pressure, placed in a metal mold of <NUM> × <NUM> × <NUM> depth, and subjected to heat treatment for <NUM> hours at <NUM> to produce a silicone resin for an acoustic wave probe (sheet of <NUM> long × <NUM> wide × <NUM> thick). Hereinafter, the silicone resin for an acoustic wave probe produced in this manner is referred to as a "silicone resin sheet".

Predetermined silicone resin sheets were produced similarly to Example <NUM> except that the composition of the polysiloxane mixture of Example <NUM> was changed to the compositions disclosed in Table <NUM>.

Truly spherical surface-treated silica particles C1, C2, T1, and T2 having an average primary particle diameter and a methanol hydrophobicity described in Table <NUM> were obtained through similar processing except that the amounts of methanol, water, and <NUM>% aqueous ammonia in a step (A1) in the example disclosed in Synthesis Example <NUM> of <CIT> were changed.

A predetermined silicone resin sheet was produced in the same manner as in Example <NUM> except that the obtained truly spherical surface-treated silica particles were used as the silica particles (C).

<NUM> pbm of a vinyl terminated diphenylsiloxane-dimethylsiloxane copolymer ("PDV-<NUM>" manufactured by GELEST, INC. with a Mw of <NUM>,<NUM> and a diphenylsiloxane amount of <NUM> mol%), <NUM> pbm of polymethylhydrosiloxane ("HMS-<NUM>" manufactured by GELEST, INC. with a Mw of <NUM>,<NUM>), and <NUM> pbm of heteromorphic surface-treated fumed silica ("AEROSIL (registered trademark) R974 manufactured by NIPPON AEROSIL CO. with an average primary particle diameter of <NUM> which is a surface-treated product with dimethyldichlorosilane (DDS) and had a methanol hydrophobicity of <NUM> mass%) were kneaded with a kneader for <NUM> hours at a set temperature of <NUM>. However, since the viscosity was too high, the kneader overloaded and stopped. Therefore, it was impossible to knead the mixture.

<NUM> pbm of a vinyl terminated diphenylsiloxane-dimethylsiloxane copolymer ("PDV-<NUM>" manufactured by GELEST, INC. with a Mw of <NUM>,<NUM> and a diphenylsiloxane amount of <NUM> mol%), <NUM> pbm of polymethylhydrosiloxane ("HMS-<NUM>" manufactured by GELEST, INC. with a Mw of <NUM>,<NUM>), and <NUM> pbm of heteromorphic non-treated fumed silica ("AEROSIL (registered trademark) <NUM> manufactured by NIPPON AEROSIL CO. with an average primary particle diameter of <NUM> without surface treatment which had a methanol hydrophobicity of <NUM> mass%) were kneaded with a kneader for <NUM> hours at a set temperature of <NUM>. However, since the viscosity was too high, the kneader overloaded and stopped. Therefore, it was impossible to knead the mixture.

<NUM> of ion exchange water and <NUM> of silica particles as samples were placed in a beaker at <NUM> and stirred with a magnetic stirrer, methanol was added dropwise thereto from a burette, and the amount (Xg) of methanol added dropwise until the whole sample settles was measured. The methanol hydrophobicity was calculated using the following equation.

The viscosity of a paste before addition of a platinum catalyst was measured using "RheoStress RS6000" which is a trade name manufactured by HAAKE under the conditions of a temperature of <NUM> and a shear rate of <NUM>-<NUM>.

In Comparative Examples <NUM> and <NUM>, it was impossible to obtain a homogeneous composition due to high viscosity, and therefore, it was impossible to measure the viscosity.

The following evaluation was performed on silicone resin sheets of Examples <NUM>-<NUM> and Comparative Examples <NUM>-<NUM>.

The type A durometer hardness of each of the obtained silicone resin sheets with a thickness of <NUM> was measured using a rubber hardness meter (trade name "RH-201A" manufactured by Excel co. ) in compliance with JIS K6253-<NUM> (<NUM>).

A trouser-type test piece of a silicone resin sheet with a thickness of <NUM> was manufactured and the tear strength was measured in compliance with JIS K6252 (<NUM>).

The density of each of the obtained silicone resin sheets with a thickness of <NUM> at <NUM> was measured using an electronic gravimeter (a trade name of "SD-<NUM>" manufactured by ALFA MIRAGE) in accordance with a density measurement method of a method A (underwater substitution method) disclosed in JIS K7112 (<NUM>). The acoustic velocity of an ultrasonic wave was measured at <NUM> using a sing-around type acoustic velocity measurement apparatus (a trade name of "UVM-<NUM> type" manufactured by Ultrasonic Engineering Co. ) in compliance with JIS Z2353 (<NUM>) and acoustic impedance was obtained from a sum of the density and the acoustic velocity which had been measured.

A sinusoidal signal (a wave) of <NUM> which had been output from an ultrasound oscillator (a function generator with a trade name of "FG-<NUM>" manufactured by IWATSU ELECTRIC CO. ) was input into an ultrasound probe (manufactured by JAPAN PROBE), and an ultrasound pulse wave with a center frequency of <NUM> was generated in water from the ultrasound probe. The magnitude of the amplitude before and after the generated ultrasonic wave passed through each of the obtained silicone resin sheet with a thickness of <NUM> was measured in a water temperature environment of <NUM> using an ultrasound receiver (an oscilloscope with a trade name of "VP-5204A" manufactured by Matsushita Electric Industrial Co. ) The acoustic (ultrasonic) attenuation of each material was compared with each other by comparing the acoustic (ultrasonic) sensitivities of each material.

In the following calculation equation, Vin represents a voltage peak value of an input wave which is generated by the ultrasound oscillator and has a half-width of less than or equal to <NUM> nsec. Vs represents a voltage value obtained when the ultrasound oscillator receives an acoustic wave (ultrasonic wave) that the acoustic wave (ultrasonic wave) generated passes through a sheet and is reflected from an opposite side of the sheet.

The obtained results were summarized and shown in Table <NUM>.

In table <NUM>, the Mw of the polyorganosiloxane (A) and the polyorganosiloxane (B) is simply described as a molecular weight, and the type of each component is indicated by a trade name.

As is apparent from Table <NUM>, in Examples <NUM>-<NUM>, the viscosity of each composition for an acoustic wave probe in a state before vulcanizing was low, and all of the silicone resins for an acoustic wave probe could obtain high resin hardness and tear strength and excellent acoustic impedance while maintaining the acoustic (ultrasonic) sensitivities ≥ -<NUM> dB.

In contrast, the viscosity of the composition for an acoustic wave probe before vulcanizing was high in Comparative Example <NUM> in which silica particles having an average primary particle diameter of <NUM> are used, and therefore, it was impossible to knead the composition. In addition, in Comparative Example <NUM> in which the content of silica particles was reduced, even though it was possible to knead the composition, it was impossible to disperse the silica particles, the silicone resin for an acoustic wave probe had poor acoustic sensitivity, and the acoustic impedance was not close to a human body. In Comparative Example <NUM> in which silica particles having an average primary particle diameter of <NUM> are used, the acoustic sensitivity is not sufficient. In Comparative Examples <NUM> and <NUM> in which silica particles having an average primary particle diameter exceeding <NUM> were used, the tear strength was low and the acoustic sensitivity was poor. In Comparative Example <NUM> in which silica particles of which the average primary particle diameter was within the range of the present invention and which were not subjected to surface treatment were used, the viscosity of the composition for an acoustic wave probe before vulcanizing was high, and therefore, it was impossible to knead the composition.

Claim 1:
The use of a composition comprising a polysiloxane mixture containing
(i) polysiloxane having a vinyl group,
(ii) polysiloxane having two or more Si-H groups in a molecular chain, and
(iii) silica particles which
- have an average primary particle diameter of <NUM>-<NUM>,
- are subjected to surface treatment, and
- have a methanol hydrophobicity (MH) of <NUM>-<NUM> mass-%, determined by adding dropwise, to <NUM> of silica particles in <NUM> ion exchange water at <NUM> and with magnetic stirring, methanol until the whole sample settles, and calculating the MH as <MAT> wherein X is the amount (g) of methanol added, for an acoustic wave probe.