JPS5856987B2 - Manufacturing method of polymer piezoelectric material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a polymeric piezoelectric material, and particularly to provide a polymeric piezoelectric material for a transducer using a film such as polyvinylidene fluoride.

Conventionally, in order to obtain a polymeric piezoelectric material having large piezoelectricity, such as polyvinylidene fluoride, there has been a method of mechanically uniaxially stretching polyvinylidene fluoride having an α-type structure to form a β-type structure. A method of crystallizing it from a polyvinylidene fluoride fermentation solution, a method of preparing it by the Han-kai method, etc. are known.

The polyvinylidene fluoride with the β-type structure described above is heated at an appropriate temperature (5
When stretched at a temperature of 0° C. or higher, a polyvinylidene fluoride film with a β-type structure can be produced.

For example, at a temperature of 50 to 120°C, this film
When an electric field of 8 degrees 1OOOK/Crft is applied and this is cooled, the molecular form changes and spontaneous polarization occurs.

If an electrode is formed on the polyvinylidene fluoride film obtained in this way and mechanical displacement is applied to this film,
It is well known that piezoelectric force is generated between the electrodes.

These conventional polymer piezoelectric polarization devices are shown in FIG.

In the example shown in FIG. 1, the film 1 with a β-type structure is
The film 1 is polarized by applying a high voltage between the stain electrodes 2 and 1 from the DC power source 3 in oil or air.

However, even if the thickness of the film 1 is made as thin as possible and the DC voltage is made as high as possible,
There is a drawback that the piezoelectric constant ga of the film 1 polarized by the method shown in FIG. 1 cannot be increased.

Therefore, the main object of the present invention is to provide a piezoelectric constant of
The object of the present invention is to provide a polymeric piezoelectric material that can greatly increase 3□.

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIGS. 2 and 3.

In FIG. 2, parts that are the same as those in FIG. 1 are given the same reference numerals, and redundant explanation thereof will be omitted.

FIG. 2 shows an apparatus for obtaining the polymer piezoelectric material of the present invention.

In FIG. 2, an insulating net, such as silk, a chemical fiber net, a net of about 10 to 500 meshes, or an insulating porous plate is placed between the polyvinylidene fluoride film 1 and the positive electrode 2. A shaped object 4 is interposed.

A high voltage is applied from a DC power supply 3 between the electrodes 2 and 2' to which the polyvinylidene fluoride film 1 and the mesh 4 are sandwiched, thereby polarizing the film 1.

Hereinafter, various embodiments of the present invention will be described in which various polarization conditions are selected.

Example 1 In the apparatus shown in FIG. 2, a polyvinylidene fluoride film 1 having a thickness of 100 μm was passed through a silk net 4 having a thickness of 80 μm with 200 to 250 meshes, and placed in silicone oil at a temperature of ˚C. A DC voltage of 10 KV is applied from the DC power supply 3 to the electrodes 2 and 2'.
Add time to polarize.

After performing this polarization treatment, the film 1 and the like are cooled while applying voltage from the DC power source 3.

After the polarization is completed, the front surface of the film 1 is washed, and aluminum is deposited on both sides of the film 1 by vacuum evaporation. When this is used as an electrode, the piezoelectric constant Llt of the film 1 is 27.
It was 0 Xl 0 3 mV/N.

Example 2 Between the minus side electrode 2' shown in FIG.
The film 1 is polarized by applying a DC voltage of 10 KV from the DC power source 3 between the electrodes 2 and 2' in silicone oil at a temperature of 85 DEG C. with a wire mesh of ~250 meshes and a thickness of 80 microns interposed therebetween.

After performing the polarization process, the film 1 and the like are cooled while applying voltage from the DC power source 3.

After the polarization was completed, the surface of the film 1 was washed, and aluminum was vacuum-deposited on the surface as an electrode.The compression constant g3t of the film 1 was 230×10 −3 mV/N.

Example 3 Positive side electrode 2 and negative side electrode 2 shown in Fig. 2
' and a β-treated polyvinylidene fluoride film 1 having a thickness of 100 μm, two wire nets having a mesh size of 200 to 250 and having a thickness of 80 μm are interposed.

Next, the other conditions were the same as in Example 2, and the piezoelectric constant ga of the polarized film 1 was 228 x 10-3 mV/N.
Met.

Example 4 The piezoelectric constant g3t of the polarized film 1 was 216XIO' mV/N under the same conditions as in Example 3 except that the temperature of the silicone oil was 80° C. and the DC applied voltage was 12 KV.

Example 5 Polyvinylidene chloride films with a thickness of 115μ and 110μ were stacked, sandwiched between electrodes 2 and 2' through one wire assembly, and a direct current was applied between the electrodes 2 and 2' in silicone oil at a temperature of 90°C. Apply a voltage of 17KV.

In this case, the piezoelectric constant gar of the film on the side of the positive electrode 2 with a thickness of 115μ is 252 The number of compressed tablets of 1 film was 251×10 mV/N.

Comparative Example 1 In the configuration shown in Figure 1, β
A DC voltage of 8 KV (the limit of polarization voltage at a temperature of 80° C.) is applied from a DC power supply 3 to the polyvinylidene fluoride film 1 having a thickness of 100 μm for 1.5 hours to polarize the film 1.

In this case, the piezoelectric constant g3r of film 1 is 192X10
-3 mV/N.

Comparative Example 2 In order to compare with Example 5, 100μ was placed on the positive electrode 2 side.
A polyvinylidene fluoride film with a thickness of 115 μm is placed on the negative electrode i side, and a similar film with a thickness of 115 μm is placed on the negative electrode i side.

The temperature of silicone oil is 90-95℃, and the DC voltage is 17KV.
The piezoelectric constant g3z of a 100μ thick film when polarized as
It was 3 mV/N.

Considering the above examples and comparison series, the piezoelectric constant g
bt is related to the product r of the DC applied voltage E and the ambient temperature T during polarization.

The piezoelectric constant characteristics of the conventional example shown in FIG. 1 and the piezoelectric constant characteristics of the embodiment of the present invention shown in FIG.
and curve 6, respectively.

In Fig. 3, the horizontal axis represents the film thickness σμ and the aforementioned γ.
The piezoelectric constant g3□ is plotted on the vertical axis.

According to the present invention, a polymer piezoelectric material having a considerably large piezoelectric constant as described above can be obtained, and the above-mentioned effect can be considered as follows.

That is, the polyvinylidene fluoride film during polarization is strongly electrostatically attracted to the positive electrode side by receiving a DC voltage.

As a result, the film is deformed due to non-uniformity in the thickness of the stretched β-type film, the state of close contact between the polarization electrode and the film, thermal shrinkage, and the like.

The non-uniform space created between the electrode and the film due to the deformation of the film is made uniform by the mesh, and the polarization voltage is applied uniformly.

In this way, the film undergoes dielectric breakdown due to the heat generated by the local concentration of the polarization electric field.

It is speculated that it may be possible to prevent this.

Interesting results were obtained in each of the above Examples.

That is, the mesh-like unevenness is completely formed in the film of Example 1 and Example 5 and the positive electrode side film of Example 3, whereas the film of Example 2 and Example In case 3, the negative electrode side film has:
Almost no mesh-like irregularities are formed.

These uneven parts formed on the surface of the film change the Young's modulus of the film, increasing the flexibility of the film against bending stress, and the uneven parts formed on the surface of the film deform and change the crystalline state. It can also be inferred that the piezoelectric constant increases due to the synergistic effect of the electrostrictive effect due to minute deformation of the molecules.

The present invention has the feature that a polymeric piezoelectric material having an extremely large piezoelectric ξ number can be obtained as described above.

[Brief explanation of the drawing]

Figure 1 shows a conventional polymer piezoelectric polarization device, Figure 2 shows a polymer piezoelectric polarization device of the present invention, and Figure 3 shows a polymer piezoelectric polarization device polarized by the present invention and a conventional polarization device. number and γ
It is a comparative characteristic curve diagram with /μ. In the figure, 1 is a film, 2 and 2' are electrodes, 3 is a DC power source, and 4 is a mesh or porous plate.

Claims (1)

[Claims] 1. A method for producing a polymer piezoelectric material, characterized in that during polarization, a net-like or porous insulating material is interposed between the material to be polarized and the polarization electrode to enhance the polarization process.