JPS58171878A - Polymer composite piezoelectric material - Google Patents

Abstract

PURPOSE:To obtain a piezo-electric element of constant acoustic impedance and high sensitivity by a method wherein a vulcanized composition constituted of conductive carbon black, rubber polymer substance, and ferrodielectric ceramic corpuscles is changed into a thermal electret. CONSTITUTION:After kneading conductive carbon black, rubber polymer substance, and ferrodielectric ceramic corpuscles, it is vulcanized and thus formed into a desired shape. Next, it is changed into a thermal electret by applying an electric field thereto. The conductive black is added to enhance the ultrasonic sensitivity without increasing acoustic impedances. By constituting in this manner, the piezoelectric body wherein the ultrasonic sensitivity is enhanced without increasing acoustic impedances can be obtained. Since the rubber in the polymer composite piezo-electric body is vulcanized, the rate of elasticity is improved without increasing acoustic impedances, and therefore the mechanic strength can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a polymer composite piezoelectric material K1g which has low acoustic impedance and excellent ultrasonic sensitivity.

Conventionally, it is well known that a piezoelectric substance has one characteristic of being a crystalline body with a center of symmetry f#9, and inorganic piezoelectric substances such as quartz crystal, Rochelle salt, and lead zirconate titanate are often used in practice. However, these piezoelectric materials have poor flexibility, so S
In addition to being extremely difficult to shape into a surface, it is also difficult to form and process, making it difficult to obtain a thin piezoelectric material. Furthermore, since the acoustic impedance is large, when used as an ultrasonic oscillator, there will be many resonance echoes, the signal will be unclear, and the transducer will be in direct contact with the medium and O.
It has major drawbacks such as poor acoustic impedance matching, which leads to a decrease in conversion efficiency.

On the other hand, the existence of piezoelectricity has been recognized in certain aIQ polymer materials, such as naturally oriented polymers such as cellulose and proteins, and g-stretched films of polyγ-methyl-L-glutamate synthetic polymers. In addition, there are some synthetic polymer electrets, such as polyvinyl fluoride! Soften a film of N resin, polyvinylidene fluoride resin, polyacrylonitrile resin, polycarbonate) 11111, etc.
It is known that the M transverse piezoelectric materials obtained by these methods have -HA properties and Due to its excellent moldability and low acoustic impedance, there are fewer resonance echoes, resulting in a clear signal.9
However, since it requires stretching and polarization, thick IA fabrics are preferred, making it suitable for ultrasonic diagnosis and i! It is difficult to create an oscillator of several MHH suitable for an ultrasonic probe, which requires special ingenuity. Since each element becomes very small and the capacitance decreases, the use of materials with low dielectric constants has the drawback that it is difficult to achieve electrical matching.

A polymer composite piezoelectric material in which sn-electronic semiconductor lIk particles are dispersed and mixed in a polymer material is known as a material that has improved these drawbacks.

For example, JP-A No. 54-5598 l1lO polymer composite piezoelectric material has a much smaller acoustic impedance than inorganic piezoelectric materials, so it is possible to obtain clear signals with fewer resonance echoes, and compared to organic piezoelectric materials. However, since there is no anisotropy in the piezoelectric constant, molding and processing can be performed freely, and furthermore, since the dielectric constant is large, it has an excellent nine complex length, which makes it easy to electrically match and deposit. However, the ultrasonic sensitivity is still lower than that of conventionally used inorganic piezoelectric materials, and improvements have been desired.

The present inventor has discovered that by applying tetraelectric carbon black to a rubber-like polymer composite piezoelectric material, the piezoelectric constant can be increased without increasing the acoustic impedance, and the ultrasonic sensitivity can be increased. By vulcanizing the rubber inside, the elastic modulus is improved with almost no increase in acoustic impedance, the constant of electromechanical bonding increases, and the tensile IJ
! The present invention was completed by discovering that a mechanical fid such as Jl& etc. can be made similar to the above.

Therefore, the purpose of the present invention is to eliminate the drawbacks of conventional inorganic and organic piezoelectric materials, while maintaining excellent moldability, low acoustic impedance, large dielectric constant, and lack of squareness in piezoelectric constant. The purpose of the present invention is to provide a polymer composite piezoelectric material which can be used as an ultrasonic element and which has a high ultra-high density δ capsule.

The polymer composite piezoelectric material of the present invention contains 5!
In a piezoelectric body made by cross-circuiting ceramic fine particles of A-electromagnetic body and forming it into a desired shape, it becomes a thermoelectret.
It is assumed that the condition is t-%.

The carbon blank used in the present invention is not particularly limited, but includes, for example, acetylene black,
Furnace black or the like is used, but Ketjenblack 11 (manufactured by Lion Maxo Co., Ltd.) is particularly preferred because it increases ultra-ta sensitivity without increasing acoustic impedance υD with a small amount of LfSυ port.
The effect of Jl + Violet increases as it increases, but at the same time it lowers the resistance 'tLt- in the thickness direction of the polymer composite,
If the volume resistivity becomes approximately 1O"Q-cs or less, the leakage 1tfi will become too large when an electric field is applied to the molded body to make it into a thermal electret!'The effective electric field will decrease.Therefore, the effective electric field will decrease. 9j of the present invention because the piezoelectric 4 becomes smaller.
J-button is no longer displayed. On the other hand, if the weight of carbon black is less than 1 part by weight with rubber, the effect of the present invention will be poor.In general, acetylene black, 7 Arnes black is used as a cover for rubber-like molecules and resin-like polymers. The appropriate amount for regular delivery is 1~A5 weight j1 inch, and the appropriate amount of Ketjen Black is 0.5~101 inch.

A method commonly used for vulcanizing 7I11VLF'i rubber may be used, and it may be used in combination with sulfur, zinc oxide, stearic acid, anti-aging agents, etc., but it is even more effective if a vulcanization accelerator is added. As vulcanization accelerators, thiazoles,
For example, 2-penzodeazole disulfide, 2-mercaptobenzothiazole, dienylguanidine, tetracyclobenzoquinone, 4,4'-dithiomorpholine, P-benzoquinone diamide, etc. are used.

Examples of rubbery diurnal molecular substances include natural rubber and 8ER.

Ethylene propylene rubber, silicone rubber, acrylonitrile-butadiene rubber, epichlorohydrin rubber, fluororubber, urethane rubber, etc. can be used. ! 1t
It is preferable to have 4 large rubber kumquats.

When using a non-polar rubber such as natural rubber or ethylene propylene rubber, the above-mentioned high d calculator rubber or the resinous polymer mentioned below is preferably one with a violet of 40 or more. It is desirable to use the mixture in such a way that the amount of water is equal to or greater than 100 ml.

This rubbery polymer can be used by adding 0 to 2000 parts by weight, preferably 900 tf parts/A, to other resinous polymers per 1 part by weight of the rubbery polymer.

Preferred resin-like polymer materials include polyvinylidene fluoride resins, polyacrylonitrile resins, polyamide resins, etc. (polyacetal resins that have a wall t1 quality of ≦1 and have a high surging resistance 4); #5I4IC4
By using a polymer material in combination with a rubber having a high viscosity, it is possible to obtain low impedance characteristics, high ultrasonic sensitivity, and an excellent mechanical A degree as a polymer pressurized body.

As the hard-bound electric material 72 mix particles, lead titanate,
Copy particles with a VILt of 40.1 to 100 μm are used, which are obtained by crushing known inorganic piezoelectric materials such as barium titanate and lead zirconate titanate, and subjecting them to IIkLJllJll. 50 for lt+uO straight lit part of polymer and carbon black
0-2000 weight 1g! As the M& method for adding silkworms, any means known as a general mixing method such as a kneader, mixing roll, extruder, plus dog 2-f, various collectors, ball mill, etc. can be conveniently used, and as a molding method, Extrusion molding method, curling molding method, etc. can be conveniently used. The round bottom shape is available in various shapes such as plate, round, and sheet shapes.
sell.

Vulcanization can be accomplished by previously vulcanizing the rubbery polymer that is added. In addition, after molding 1 rubber-like polymer, 1 shield-like molecule, and ceramics, 0
To make a billion - possible.

However, when used in combination with a resinous polymer with a high softening point,
Rubber-like polymer is pre-vulcanized in order to prevent sudden vulcanization and inhibition of component separation when mixing 4M of rubber-like polymer and 11 rod-like polymer. It is advisable to use vulcanization, and in the case where preliminary vulcanization has been performed, an operation is performed to complete the vulcanization after pressure vulcanization.

In order to impart pressure properties to the molded body, the molded body was
*In a Q-disturbed state, an electric field is applied from the six members of the molded body to a DC electric field or an alternating current electric field for a certain period of time, and then the body 1 is cooled and the electric field is removed, thereby converting it into a thermal electret. I do.

aFitt-1 for thermal electretization, below mK at which the polymer substance starts flowing, generally from Vio to 150'C, preferably from 1 to +000. The electric field is usually applied using four layers of gold I on the surface of the molded body! 4 foil, conductive resin,
A gold A coating formed by a four-electrode Bernet, Rurui, or vacuum evaporation layer or chemical plating is used as an electrode, and the electric field is generally set at rt.
The electric field is preferably from 10 kV/am to 300 kV/cym so as not to cause dielectric breakdown, and the time is not limited to d%, but it is preferably 10 minutes or more.

Next, examples of the present invention will be described, but the present invention is not limited thereto.

In the example, the piezoelectric constant (d, , ) was 130Ei, and the 1 ratio calculation calculator C-/a.) was added by #1 at 1 kHz. Further, the f4 impedance (1) and the ultrasonic wave impedance were measured using a Miill time interval meter 50531i manufactured by Panametrics.

Practical Meat 1 (1) Acrylonitrile-butadiene rubber (PM Cam, Nippon Gosei Rubber Co., Ltd.) I/C conductive carbon black (Lion Akzo Kechenbrarek 1110) and Karo hawk agent,
A vulcanization accelerator and the like were added, and the mixture was kneaded at 10° C. using a mixing roll. The mixing ratio is as follows.

PM, 3OA 2) F Ketjen Black 10 1.5F, 4* (mji Kagaku') 8.06t stearin relative (Wamotojunken granular) - 0,2F zinc ironide (Shoichicho Kagaku)
O, ey (2) The i4 prepared product in (1) above was vulcanized for 5 minutes in a mixing roll heated to 1550°C.

(3) Polyacetal resin (DuPont Delrin 500) on a heated mixing roll to 185°C
At about 12 ft'' gas average - Kg, the blend 18F prepared in Boku (2) was added little by little, and lead zirconate titanate (particle size of 0.5 to 10 μm, average particle size of 2 μyn) was added 323 f. Add the ingredients little by little and mix evenly.

(4) Using a compression press heated to 190°C, 10 t:xi was obtained from the polymer composite prepared in (3) above.
A sheet with a size of x 10 car x 200 μm was prepared.

Electrodes were provided on both sides of this sheet by gold vapor deposition.

(5) 4t) g in the above (4) in an oven heated to C.
A! A DC electric field of 4,000 V was applied to the front and back of the sheet for 1 hour, and after cooling to room temperature, the electric field was changed to a thermal electret.
0 k 'I/cxa required・'(5) Above <5)
The performance of the polymer composite piezoelectric material prepared in the above was evaluated and the nine values obtained are shown in Table 1.

Comparative Example 1 11! Same as Example 1 except that nothing was added to the rubber in step (1) of Example 1! Table 1 shows the results of measuring performance 1 of the polymer composite piezoelectric material measured by iL [Phase] Comparative Example 2 Example 1 except that conductive carbon black was not added in step (1) of Example 1. Table 1 shows the results of measuring the performance of the polymer composite piezoelectric material prepared in the same manner as above.

Comparative Example 3 A high-density polymer obtained by adjusting fA in the same manner as in Example 1 except that only conductive carbon black was added to the rubber in step (1) of Example 1, and neither vulcanizing agent nor vulcanization accelerator was added. The performance of the molecular composite piezoelectric material was measured and nine results are shown in Table 1.

Compared to Comparative Example 1, the ultra-f wave sensitivity is significantly improved without changing the 1iFl# impedance.

Part 1 Example 2 The performance of the polymer composite piezoelectric material obtained by adjusting the polyacetal resin and the blended material in step (3) of Example 1 in the same manner as in Example 1 except that the interest rate of the polyacetal resin and the blend was varied was evaluated. The measured results are shown in Table 2.

2. However, according to the present invention, conductive carbon black, a rubbery polymeric substance, and strong electric ceramic fine particles are mixed together. , and since the vulcanized composition is made into a thermoelectret, it has excellent moldability, low acoustic impedance, and large n1L4. Jl! has high ultrasonic sensitivity while maintaining the absence of anisotropy in the piezoelectric 4! This has the effect of being able to provide a polymer composite piezoelectric material through which a single sound wave can pass.

1 ~1 Daikojin benban clay stone door, fu c1:,・,ノ

Claims (1)

[Claims] A polymer composite piezoelectric material containing electrically conductive carbon black, a rubber-like polymeric substance, and strong electric ceramic fine particles, and obtained by converting a vulcanized composition into a thermal electret.