JPS6239551B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a composite piezoelectric film made of a polymeric material and an inorganic ferroelectric powder, and a method for manufacturing the same. The present invention relates to a composite piezoelectric film body in which the concentration of inorganic ferroelectric powder is continuously varied in the film thickness direction, and a method for manufacturing the same.

Conventionally, inorganic crystals such as quartz crystal and Rothsiel salt, and ceramics such as lead titanate and lead titanium zirconate are well known as substances having a piezoelectric effect.
Although these piezoelectric materials all have a large piezoelectric effect, they are hard, brittle, and difficult to process, so it has been extremely difficult to create thin films with large area piezoelectric bodies or flexible piezoelectric bodies. . Furthermore, in biological ultrasound probes using piezoelectric inorganic crystals or ceramics, the acoustic impedance differs greatly from that of the living body. It had to be integrated by gluing, etc.

On the other hand, although it has been confirmed that piezoelectricity can be maintained in uniaxially stretched films of amino acid polymers such as polybenzyl glutamate, and organic materials such as polyvinyl chloride and polyamide, the piezoelectric effect is small in all of them, and the piezoelectric effect is the largest. Even with β-type polyvinyritene fluoride, which is considered to be a biological ultrasonic probe, the impedance matching with the living body is good, but the elongation piezoelectric constant (d ₃₁ ) is 2.5 × 10 ^-12c /
N, the piezoelectric constant (d ₃₃ ) of thickness vibration is 3.1×10 ^-12c /N
It was nothing more than

Also, attempts have been made to use a composite piezoelectric film body in which inorganic ferroelectric powder is dispersed as uniformly as possible in a polymer material as a piezoelectric element for a keyboard.
Particularly, in the case of a type in which pressure is applied by impact, a complicated process such as separately providing a protective layer on the surface of the piezoelectric element is required.

In view of the above-mentioned drawbacks, the present invention is easy to form into a thin film, has a large piezoelectric effect, is highly flexible, has little change over time, and has impedance matching with a living body as an ultrasonic probe for living bodies. Composite piezoelectric film body with good properties, or composite piezoelectric film body in which a protective layer is integrally molded in a piezoelectric element for a keyboard, that is, a composite piezoelectric film body in which the concentration of inorganic ferroelectric powder is continuously varied in the film thickness direction. The purpose is to provide a method for producing the same. The composite piezoelectric film body of the present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a cross-sectional view of the structure of a composite piezoelectric film body according to the present invention, in which an inorganic ferroelectric powder 2 is arranged in a composite piezoelectric film body 1. As shown in FIG. Figure 2 shows the acoustic impedance in the film thickness direction of the composite piezoelectric film body based on the present invention.
Since its concentration changes continuously in the film thickness direction, the acoustic impedance also changes continuously. Therefore, as shown in FIG. 1, by arranging the polymer material layer 3 side on the living body side as an ultrasound probe for living body, it is possible to form an excellent piezoelectric element for an ultrasound probe for living body. can.

Further, when used as a keyboard, by using the polymer material 3 side as a protective layer, the piezoelectric portion and the protective layer can be integrally molded to obtain a product.

When used for a keyboard, it is preferable to use an inorganic ferroelectric powder whose concentration changes more rapidly in the film thickness direction (that is, one to which sufficient centrifugal force is applied).

It goes without saying that the degree of change in the concentration of the inorganic ferroelectric powder can be adjusted as appropriate by selecting the particle size and specific gravity of the inorganic ferroelectric powder, the specific gravity viscosity of the polymer material, centrifugal force, etc.

Next, the method of the present invention will be explained using FIG. 3 showing a specific example of the apparatus.

In FIG. 3, one end of the cylinder 4 is connected to the rotating part 5. The inner surface of the cylinder 4 is sufficiently smooth, and according to the present invention, the polymer material and inorganic ferroelectric mixed solution 6 is applied to the inner surface of the cylinder 4 using an applicator 7 using centrifugal force. That is, the method of the present invention converts inorganic ferroelectric powder such as PbTiO ₃ type or PZT type into polyvinylidene fluoride (hereinafter referred to as PVDF), polyvinylidene fluoride-ethylene trifluoride (hereinafter referred to as PVDF-TrFE), etc. This mixed solution is applied in the form of a film by centrifugal force, and when the concentration of the inorganic ferroelectric powder changes continuously in the film thickness direction due to centrifugal force. By solidifying and molding, a composite piezoelectric film body as shown in cross section in FIG. 1 is obtained. Next, electrodes are provided on both sides of the membrane body, and a high voltage is applied between these front and back electrodes to perform appropriate polarization treatment.

More specifically, the composite piezoelectric film body and the manufacturing method thereof based on the present invention are described in more detail. The mixed solution is mixed and dispersed in a polymeric material, applied to the substrate by centrifugal force, and removed from the substrate after drying. Electrodes such as Ag are installed on both surfaces by vacuum evaporation, etc. By applying a direct current electric field of about 100 KV/cm at a temperature below the point, it is possible to form a composite piezoelectric film in which the concentration of inorganic ferroelectric powder changes continuously in the film thickness direction. By separating the membrane coated onto the substrate using centrifugal force from the substrate before the organic solvent has completely dried, and performing a stretching process, not only can the mechanical strength of the membrane be greatly improved. When a polar polymer material is used, the piezoelectric effect can also be improved.

The inorganic ferroelectric powder used in the present invention has the general formula (A ²⁺ B ⁴⁺ O ₃ , A ¹⁺ B ⁵⁺ O ₃ ,
Examples include those having a perovskite structure represented by A ³⁺ B ³⁺ O ₃ ), and the amount thereof can be practically set at 20 to 90% by weight.

According to the present invention as described above, the piezoelectric effect is large,
It is possible to obtain a composite piezoelectric film that is highly flexible, has excellent change over time, and in which the concentration of the inorganic ferroelectric powder changes continuously in the film thickness direction. Therefore, it is noteworthy that the impedance matching with the living body is excellent even as an ultrasonic probe for living bodies, and there is no need to provide a matching layer by adhesion or the like. Moreover, when used as a piezoelectric element for a keyboard, a protective film can be integrally formed, and it can be said to be of great practical value.

Hereinafter, the present invention will be explained in detail with reference to Examples.

<Example 1> First, 500 gr of spherical PZT fine powder with an average particle size of 5 μm as an inorganic ferroelectric fine powder was mixed and dispersed in 1 kg of a 20% by weight PVDF-dimethylforramide solution using a hole mill. This mixed solution is placed on the inner surface of a cylinder fixed to a rotating shaft, and the rotation speed is gradually increased from 75 to
By changing the speed up to 420 rpm, we formed a composite piezoelectric film in which the concentration of inorganic ferroelectric powder changes continuously in the film thickness direction using centrifugal force and the difference in specific gravity. After removing the film from the inner surface of the cylinder with some dimethylformamide remaining in the film and biaxially stretching it to 1.5 times,
After drying under reduced pressure, both sides of this membrane were coated with 3.5
After installing the Ag electrode in a vacuum below ×10 ^-6 torr,
200K.V./between electrodes for 1.5 hours in a constant temperature bath at 120℃
A DC electric field of cm was applied for 2 hours, and the polarization operation was completed by cooling to room temperature while applying the voltage, to obtain a composite piezoelectric film. When the piezoelectric properties of this membrane were measured, the piezoelectric constant of elongation _d31 was 5.3×10 ^-11c /
N, the piezoelectric constant d ₃₃ of thickness vibration is 8・9×10 ^-11c /
It was N. Note that whether or not the concentration of the inorganic ferroelectric powder in the composite piezoelectric film body based on this example changes continuously in the thickness direction can be determined by sequentially wrapping the film body and checking the film thickness at the time of wrapping and the film body. This was confirmed by measuring the specific gravity of

Next, using this composite piezoelectric film body, we measured the ultrasonic characteristics (by emitting ultrasonic waves into water and observing the reflection from the acrylic plate in the water), and the results showed that the impedance matching was good and the characteristics were high sensitivity. An ultrasonic probe with

It also showed good characteristics when used as a piezoelectric element for a keyboard that applies pressure by impact.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a composite piezoelectric film body according to the present invention. 1... Composite piezoelectric film body, 2... Inorganic ferroelectric powder, 3... Polymer material. FIG. 2 is a curve diagram showing the acoustic impedance in the film thickness direction of the composite piezoelectric film body according to the present invention, and FIG. 3 is a partially cutaway perspective view showing an example of a device using the method of the present invention.

Claims (1)

[Claims] 1. In a composite piezoelectric film body made of inorganic ferroelectric powder dispersed in a polymeric material, the concentration of the inorganic ferroelectric powder is continuously changed in the film thickness direction. Features a composite piezoelectric film body. 2. Forming a mixed solution made of a polymeric material in which inorganic ferroelectric powder is dispersed into a film by centrifugal force;
A method for manufacturing a composite piezoelectric film body, comprising the step of solidifying and forming the inorganic ferroelectric powder when the concentration of the inorganic ferroelectric powder continuously changes in the film thickness direction due to the centrifugal force.