POROUS PIEZOELECTRIC MATERIAL MOLDED BODY, METHOD OF MANUFACTURING SAME, AND PROBE USING SAID MOLDED BODY

Abstract

[Object] To provide a porous piezoelectric material molded body highly useful as a constituent material of a piezoelectric transducer suitable, in particular, for a probe of medical ultrasound diagnosis equipment. [Solution] A porous piezoelectric material molded body, in which 1000 or more spherical pores with an average pore diameter in the range of 2 to 70 μm are dispersedly formed per volume of 1 mm3, is characterized in that there is substantially no pore with a pore diameter larger than 50 μm, and 80% by volume or more of the total pores that constitute a spherical pore group have a pore diameter within ±20% of the average pore diameter.

Claims

1. A porous piezoelectric material manufacturing method for a powder molded body made of piezoelectric material, comprising: under conditions that a powder molding die is close-packed with spherical piezoelectric material particles or coated composite particles obtained by coating a spherical pore-forming material with piezoelectric material, filling a space, which is formed between the particles regularly arranged, with spherical fine particles made of piezoelectric material in a case of the coated composite particles or spherical pore-forming material particles in a case of spherical piezoelectric particles, as required, to control porosity.

2. The porous piezoelectric material manufacturing method including claim 1, wherein material filled in the space formed between the particles have a particle diameter that is 0.155 times the diameter of the particles or less.

3. The porous piezoelectric material manufacturing method including claim 1 or 2, wherein upper and lower limits of the particle diameter of material filled in the space formed between the particles is set in a range from and below 0.155 times the diameter of the particles.

4. A porous piezoelectric material molded body including claim 1, wherein 1000 or more spherical pores with an average pore diameter in a range of 2 to 70 μm are dispersedly formed in the piezoelectric material per volume of 1 mm3, the number of pores with a pore diameter larger than 50 μm is 1% or less on a number basis, and 80% by volume or more of total pores that constitute a spherical pore group have a pore diameter within ±20% of the average pore diameter.

5. The porous piezoelectric material molded body according to claim 4, wherein 90% by volume or more of the total pores that constitute the spherical pore group have a pore diameter within ±20% of the average pore diameter.

6. The porous piezoelectric material molded body according to claim 4, wherein 80% by volume or more of the total pores that constitute the spherical pore group have a pore diameter within ±10% of the average pore diameter.

7. The porous piezoelectric material molded body according to claim 4, wherein 90% by volume or more of the total pores that constitute the spherical pore group have a pore diameter within ±10% of the average pore diameter.

8. A method of manufacturing a molded body of the porous piezoelectric material according to claim 1, comprising the steps of: preparing a coated composite particle group formed of coated composite particles obtained by coating pore-forming material particles having an average particle diameter in a range of 2 to 70 μm, each having a particle diameter within ±20% of the average particle diameter, with a mixture of a piezoelectric material powder having an average diameter in a range of 1/100 to 1/5 of the average particle diameter of the particles and a binder, wherein coated composite particles with particle diameter distribution within ±50% of average particle diameter of the coated composite particle group account for over 60% by volume of total coated composite particles that constitute the coated composite particle group; obtaining a molded body by pressure molding of the coated composite particle group; and calcining the molded body to remove the pore-forming material particles and the binder, and sintering the molded body.

9. A method of manufacturing a molded body of the porous piezoelectric material according to claim 1, comprising the steps of: producing pore-forming material particles coated with a mixture of a powder and a binder (coated composite particles) by coating pore-forming material particles having an average particle diameter in a range of 2 to 70 μm, each having a particle diameter within ±20% of the average particle diameter, with a mixture of a piezoelectric material powder having an average diameter in a range of 1/100 to 1/5 of the average particle diameter and a binder; subjecting the coated composite particle group to a particle diameter sorting process to collect a coated composite particle group consisting of coated composite particles with particle diameter distribution within ±10% of average particle diameter of the coated composite particle group; obtaining a molded body by pressure molding of the coated composite particle group collected; and calcining the molded body to remove the pore-forming material particles and the binder, and sintering the molded body.

10. An array probe, comprising: a piezoelectric transducer array including an array of piezoelectric transducers made of the porous piezoelectric material molded body of claim 4; an acoustic matching layer arranged on a surface of the piezoelectric transducer array; a backing material arranged on a back surface of the piezoelectric transducer array; and an acoustic lens arranged on a surface of the acoustic matching layer

11. A probe which is an array element probe used for ultrasound diagnosis equipment, wherein a piezoelectric material molded body used for the probe is made of porous ceramic.

12. The probe including claim 11, wherein, in the porous ceramic, 1000 or more pores are present separately and independently from one another per cubic millimeter.

13. The probe including claim 11 or 12, wherein porosity of the porous ceramic is in a range of 0.1 to 15%, preferably in the range of 0.1 to 10%.

14. The probe including any one of claims 11 to 13, wherein material of the porous ceramic used is two-component PZT or three-component PZT.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0132] FIG. 1 is a conceptual diagram illustrating an example of the structure of a porous piezoelectric material molded body according to the present invention.

[0133] FIG. 2 is a diagram for explaining the concept of obtaining a basic molded body by close-packing coated composite particles used for manufacturing the porous piezoelectric material molded body of the present invention.

[0134] FIG. 3 is a conceptual diagram illustrating, as a two-dimensional diagram, an arrangement of coated composite particles in a process of obtaining a molded body of a coated composite particle group illustrated in FIG. 2.

[0135] FIG. 4 is a conceptual diagram illustrating a process of obtaining a molded body by pressing a coated composite particle group with added piezoelectric material particles (granule) used in an example of the production of the porous piezoelectric material molded body according to the present invention.

MODES FOR CARRYING OUT THE INVENTION

[0136] In the following, a porous piezoelectric material molded body and a manufacturing method thereof of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a conceptual diagram illustrating an example of the structure of a porous piezoelectric material molded body according to the present invention. In FIG. 1, a porous piezoelectric material molded body 1 of the present invention includes a sintered body of piezoelectric material powder 11 and a number of fine spherical pores 12 which are scattered inside the molded body in a substantially aligned state (i.e., present as being uniformly dispersed). Although FIG. 1 illustrates a two-dimensional conceptual view, a three-dimensional conceptual view can be illustrated similarly.

[0137] As a most common example of piezoelectric material powder for obtaining a sintered body of piezoelectric material powder constituting the porous piezoelectric material molded body of the invention, lead-zirconate titanate (PZT) powder may be cited. However, the piezoelectric material powder is not limited to the two-component PZT or the three-component PZT, and any powder material that exhibit piezoelectricity can be used without particular limitation. As to usable piezoelectric material powders, a detailed description can be found in Patent Documents 1 to 3, the contents of which are incorporated herein by reference.

[0138] In addition, an aggregate of hollow piezoelectric material particles may also be used as the piezoelectric material powder.

[0139] Preferably, the piezoelectric material powder has an average diameter in the range of 1/100 to 1/5 of the average particle diameter of pore-forming material particles (described later). In other words, piezoelectric material particles constituting the piezoelectric material powder need to have a powder diameter sufficiently smaller than that of the pore-forming material particles, and an aggregate of piezoelectric material powders having a powder diameter as uniform as possible is preferred.

[0140] FIG. 2 is a conceptual diagram for explaining a process of obtaining a molded body by pressing a coated composite particle group used for manufacturing the porous piezoelectric material molded body of the present invention.

[0141] In the process of manufacturing the porous piezoelectric material of the invention, as described above, in the first step, coated composite particle powder is prepared; the coated composite particle powder is formed of a coated composite particle group obtained by coating pore-forming material particles having an average particle diameter in the range of 2 to 70 μm, each having a particle diameter within ±20% of the average particle diameter (i.e., particles highly uniform in particle diameter), with a mixture of a piezoelectric material powder having an average diameter in the range of 1/100 to 1/5 and a binder such that coated composite particles with particle diameter distribution within ±50% of the average particle diameter of the coated composite particle group account for over 60% by volume of the total coated composite particles constituting the coated composite particle group.

[0142] As the pore-forming material particles used in the first step, synthetic resin particles such as spherical carbon powder (spherical carbon particles), spherical polymethylmethacrylate particles, and thermosetting epoxy are generally used. Other examples of the pore-forming material particles that can be used for the manufacture of the porous piezoelectric material molded body of the invention can be found in the above-mentioned Patent Documents 1 to 3, the contents of which are incorporated herein by reference.

[0143] Incidentally, the pore-forming material particles having an average particle diameter in the range of 2 to 70 μm, each having a particle diameter within ±20% of the average particle diameter (i.e., particles highly uniform in particle diameter), are available from companies such as Nippon Carbon Co., Ltd., Soken Chemical & Engineering Co., Ltd., Japan Exlan Co., Ltd., IBIDEN Co., Ltd., and Gun Ei Chemical Industry Co., Ltd. the pore-forming material particles can also be easily obtained, if necessary, by classifying spherical pore-forming material particles obtained from a desired company with a commercially available precision classifier (precision sieve).

[0144] Examples of the binder used in the above-mentioned first step include, but are not limited to, a mixture of polyvinyl alcohol as an aqueous solution and a water-soluble acrylic resin. Other examples of the binder can be found in detail in the above-mentioned Patent Documents 1 to 3, the contents of which are incorporated herein by reference.

[0145] The coated composite particle group coated with a mixture of a powder of piezoelectric material particles and a binder can be produced by, for example, dispersing a powder of piezoelectric particles in a binder prepared as a dilute aqueous solution to obtain a slurry, and then spray-drying the slurry and pore-forming material particles using a spray dryer such as a spray-drying atomizer. As to the process of producing a coated composite particle group coated with a mixture of a piezoelectric material powder and a binder by using spray-drying of a slurry of a binder aqueous solution, in which piezoelectric particles are dispersed, and pore-forming material particles, detailed descriptions can be found in the above-mentioned Patent Documents 2 and 3, the contents of which are incorporated herein by reference.

[0146] In the process of producing a coated composite particle group coated with a mixture of a piezoelectric material powder and a binder to manufacture the porous piezoelectric material molded body of the invention, it is preferable to appropriately adjust the concentration of the binder aqueous solution, the mixing ratio of the binder aqueous solution and the piezoelectric material powder, spray-drying (or spray-granulation) conditions, and the like to obtain a coated composite particle group with a uniform particle diameter, in which coated composite particles with particle diameter distribution within ±50% of the average particle diameter of the coated composite particle group account for over 60% by volume (preferably over 80% by volume) of the total coated composite particles of the coated composite particle group.

[0147] However, there may be a case where it is difficult to obtain a coated composite particle group, in which coated composite particles whose particle diameter distribution is within ±50% of the average particle diameter of the coated composite particle group account for over 60% by volume of the total coated composite particles of the coated composite particle group by appropriately adjusting the concentration of the binder aqueous solution, the mixing ratio of the binder aqueous solution and the piezoelectric material powder, spray-drying conditions, and the like In the process of producing the coated composite particle group coated with a mixture of the piezoelectric material powder and the binder. In such case, a step of subjecting the obtained coated composite particle group to a known particle diameter sorting process can be additionally performed to collect a coated composite particle group in which coated composite particles with particle diameter distribution within ±50% of the average particle diameter of the coated composite particle group account for over 60% by volume (preferably over 80% by volume) of the total coated composite particles of the coated composite particle group.

[0148] A precision classifier such as, for example, an ultrasound precision classifier manufactured and sold by a classifier manufacturing company such as Aisin Nano Technologies Co., Ltd. can be used to perform the particle diameter sorting process.

[0149] In a case where the mixing of particles other than coated composite particles, i.e., the mixing of granule consisting of piezoelectric material alone, is disadvantageous, the above process can also be performed using an aerosol mass spectrometer manufactured and sold by KANOMAX Japan Inc.

[0150] The coated composite particle group, in which coated composite particles with particle diameter distribution within ±50% of the average particle diameter of the coated composite particle group account for over 60% by volume of the total coated composite particles of the coated composite particle group is then subjected to a step of pressing to obtain a molded body.

[0151] FIG. 3 illustrates an image of a pressure molding process of a coated composite particle group coated with a mixture of a piezoelectric material powder and a binder used for the manufacture of the porous piezoelectric material molded body of the invention. As illustrated in FIG. 3, the coated composite particles 13 are placed in the molding die to be subjected to pressure molding. Regarding the pressure molding of the coated composite particles 13 coated with a mixture of piezoelectric material particles and a binder, detailed descriptions can be found in the above-mentioned Patent Documents 2 and 3, the contents of which are incorporated herein by reference.

[0152] The molded body obtained by the pressure molding of the coated composite particle powder is then calcined at a temperature higher than the thermal decomposition temperature of the pore-forming material particles. The pore-forming material particles and the binder are burned and removed by the calcination. After that, the molded body is sintered by further heating it at a high temperature. As to the process of burning and removing the pore-forming material particles and the binder through the calcination of the molded body obtained by the pressure molding of the coated composite particle group and the sintering process, detailed descriptions can be found in the above-mentioned Patent Documents 2 and 3, the contents of which are incorporated herein by reference.

[0153] Note that when it is desired to obtain a porous piezoelectric material molded body with a low porosity as the one produced by the method described above, such a molded body can be obtain by preparing a mixture of a piezoelectric material fine powder and coated composite particles in a volume ratio of the former to the latter, for example, within the range of 1/1 to 1/10, and then pressure molding this mixture in the step of pressure molding the coated composite particle group to obtain a molded body. That is, the porosity of the porous piezoelectric material molded body can be artificially finely adjusted by using such a molded body manufacturing method.

[0154] A wet process may also be used for the purpose of obtaining a porous piezoelectric material molded body with a low porosity.

[0155] In this embodiment, a water-soluble binder is used to prepare a slurry of PZT fine powder for producing PZT-coated composite particles. For this reason, the coated composite particles is very sensitive to moisture. Accordingly, a hydrophobic solution such as, for example, acetone is sprayed on the surface of the coated composite particles. After the coated composite particle group whose surface has been pre-processed in this manner is placed in a desired mold, the space formed between the coated composite particles is filled with a slurry of PZT fine powder prepared by using a water-soluble binder. With this, a porous piezoelectric material molded body with a low porosity can be obtained.

[0156] The slurry of PZT fine powder may be prepared by a mixture of a piezoelectric material fine powder and coated composite particles/a water-soluble binder and a PZT fine powder in a volume ratio of the former to the latter, for example, within the range of 1/1 to 1/10. That is, the porosity of the porous piezoelectric material molded body can be freely adjusted by using such wet-process manufacturing method of a molded body.

[0157] When space formed between the coated composite particles is filled with a slurry of PZT fine powder prepared by using a water-soluble binder, the filling process can be performed more efficiently if the entire molding die is brought into a reduced pressure environment by a vacuum pump or the like.

EXAMPLE 1

[0158] As a piezoelectric material particle powder, PZT powder (two-component PZT powder) having a particle diameter in the range of 0.1 to 1 μm was selected. Next, 50 parts by mass of this PZT powder was mixed with 50 parts by mass of a binder aqueous solution (a mixture of an aqueous solution of 1 wt % polyvinyl alcohol and an aqueous solution of 1 wt % water-soluble acrylic resin) to prepare a PZT powder slurry. Besides, a spherical carbon powder having a particle diameter of about 10 μm (average particle diameter of 10 μm with particle diameter distribution within ±50%) was separately prepared. By spray-drying 100 parts by mass of the above PZT powder slurry and 100 parts by mass of carbon powder having a particle diameter of about 10 μm using a spray-drying atomizer, coated composite particles (average particle diameter: 20 μm) formed of PZT powder and a binder and coated with a coating layer having a thickness of about 5 μm was obtained. Then, the particle diameter distribution of the coated composite particles was measured, and it was found that it did not correspond to a coated composite particle group, in which coated composite particles with particle diameter distribution within ±50% of the average particle diameter of the coated composite particle group accounted for over 60% by volume of the total coated composite particles of the coated composite particle group. Accordingly, classification was performed using an ultrasound classifier to collect a coated composite particle group in which coated composite particles with particle diameter distribution within ±50% of the average particle diameter of the coated composite particle group accounted for over 60% by volume of the total coated composite particles of the coated composite particle group. The coated composite particles collected by the classification were placed in the molding die 14 as illustrated in FIG. 2, and the pressure molding process was performed by applying a pressure of 1 to 1.5 ton/cm2 to the coated composite particles to obtain a molded body. Incidentally, the presence of voids inside the molded body obtained by the pressure molding process could not be visually observed under a high-magnification microscope. The dispersion of the coated composite particle fine powder in the molding die is illustrated as a conceptual diagram in FIG. 3. Thereafter, the molded body obtained by pressing or compacting the coated composite particle group was pre-calcined in air at 450° C. for 1 hour to sublimate and remove carbon particles, and then calcined (sintered) at 1250° C. to thereby obtain a porous PZT molded body (sintered body), in which spherical pores having an average pore diameter of about 10 μm were formed in a three-dimensional arrangement at the position where the carbon particles were present. After cutting the porous PZT molded body and polishing the cut surface, the distribution of the pore diameter of pores appearing on the cut surface was examined. As a result, it was found that the pore diameters of 90% by volume or more of pores constituting a pore group were distributed within ±10% of the above-mentioned average pore diameter (about 10 μm).

[0159] It was also found that the distance between two spherical pores present adjacent to each other via a piezoelectric material region was distributed within the range of ±20% over 60% of the total internal region. Then, the density of the obtained porous PZT molded body was measured. As the density was 5.25 g/cm3, when calculated in consideration of the density of PZT used (6.70 g/cm3), the porosity was found to be 22% by volume. In addition, the number of spherical pores with an average pore diameter in the range of 2 to 50 μm formed inside the porous PZT molded body was examined by X-ray CT observation. As a result, it was found that there were 1000 or more of them per 1 mm3 of volume.

EXAMPLE 2

[0160] Using the same method as described in Example 1, a powder of coated carbon particles (average particle diameter: 14 μm) formed of PZT particle powder and a binder and coated with a coating layer having a thickness of about 2 μm was obtained. After that, classification was performed to collect a coated composite particle group in which coated composite particles with particle diameter distribution within ±50% of the average particle diameter of the coated composite particle group accounted for over 80% by volume of the total coated composite particles of the coated composite particle group.

[0161] Besides, PZT fine powder particles (granules) having a particle diameter of 1 to 2 μm (a particle diameter of about 15% of the coated composite particles) were separately prepared using PZT powder in the range of 0.1 to 1 μm.

[0162] 100 parts by volume of the coated composite particles collected by the classification were placed in a raw material supply hopper. Subsequently, 50 parts by volume of the above-mentioned granules prepared separately were put in the hopper. Vibration was applied to them by a vibrator attached to the hopper. When the granules put in later disappeared, the on-off valve located at the bottom of the hopper was opened to inject the piezoelectric raw material inside the hopper into a molding die through a supply pipe.

[0163] As in Example 1, the piezoelectric raw material placed in the molding die was molded (the dispersion of the coated composite particles 13 and the PZT particles (granules) 15 in the molding die 14 is illustrated as a conceptual diagram in FIG. 4), and pre-calcined and then calcined to obtain a porous PZT molded body. The density of the obtained porous PZT molded body was measured. As the density was 6.85 g/cm3, when calculated in consideration of the density of PZT used (7.60 g/cm3), the porosity was found to be 10% by volume.

[0164] After cutting the porous PZT molded body and polishing the cut surface, the distribution of the pore diameter of pores appearing on the cut surface was examined. As a result, it was found that the pore diameters of 90% by volume or more of pores constituting a pore group were distributed within ±10% of the above-mentioned average pore diameter (about 10 μm).

[0165] It was also found that the distance between two spherical pores present adjacent to each other via a piezoelectric material region was distributed within the range of ±20% over 60% of the total internal region. In addition, the number of spherical pores with an average pore diameter in the range of 2 to 50 μm formed inside the porous PZT molded body was examined by X-ray CT observation. As a result, it was found that there were 1000 or more of them per 1 mm3 of volume.

EXPLANATION OF SYMBOLS

[0166] 1 Porous piezoelectric material molded body [0167] 11 Piezoelectric material [0168] 12 Pore [0169] 13 Coated composite particle [0170] 14 Molding die [0171] 15 Piezoelectric material fine powder particle (granule)