JPS6027198B2 - Piezoelectric polymer composite material and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention produces barium titanate particles by mixing barium titanate particles having a needle-like or plate-like particle shape extending in the a-ball direction with a piezoelectric polymer compound and molding the mixture. By orienting a part or almost all of it in a certain plane or in a certain direction in a piezoelectric polymer compound and then polarizing it, it can be made into a composite material made of conventional barium titanate-piezoelectric polymer compound. The present invention aims to provide a composite material with a relatively large piezoelectric constant and a method for manufacturing the same.

Piezoelectric materials are widely used as filters, oscillators, ultrasonic transducers, surface acoustic wave elements, etc.
Most of them use ceramics such as barium titanate and lead zirconate titanate (PZT).

On the other hand, synthetic polymer compounds such as polyvinylidene fluoride, polyvinyl chloride, polyvinyl fluoride, and nylon are also known to have piezoelectric properties, and these piezoelectric polymer materials have moldability and processability that ceramics do not have. Because of its many characteristics, such as the ability to be used in the form of a film, it is used in the acoustic field such as speakers, headphones, and microphones, and in the ultrasound-related field such as ultrasound probes and ultrasound microscopes. In addition, it is expected to be applied in many fields such as keyboards and blood pressure monitors, but because the piezoelectric constant is not very large, it has only been put into practical use in parts such as speakers. In order to roughly increase the piezoelectric constant, in recent years there has been active development of so-called piezoelectric polymer composite materials in which ceramic fine particles such as barium titanate particles and PZT particles are mixed with a piezoelectric polymer compound. Piezoelectric polymer composite materials also have good moldability and
It is a material that can be expected to have many applications because it is easy to process, has moderate coagulability, and can be formed into a film. Although the piezoelectric constant has increased several times by combining ceramic particles and piezoelectric polymer compounds, an even larger piezoelectric constant is currently desired for practical use. The present invention aims to provide a piezoelectric constant of a composite material made of barium titanate particles and a piezoelectric polymer compound compared to conventional materials, a piezoelectric polymer composite material, and a method for manufacturing the same. It is.

Conventionally, barium titanate particles were difficult to produce in the form of needles or plates because the barium compounds used as starting materials, such as titanium dioxide and barium carbonate, did not have a specific shape. .

Therefore, it has been considered impossible to orient barium titanate particles in a fixed direction or in a fixed plane within a emissive polymer compound.

The present invention provides a piezoelectric polymer in which a part or almost all of the barium titanate particles are oriented in a certain plane or in a certain direction, and a method for producing the same. That is, from hydrous titanium dioxide acicular particles obtained by acid-treating potassium titanate fibers to remove the potassium component, or from anatase-type titanium dioxide particles elongated in the a-axis direction obtained by heat-treating the same, By mixing the powder and the barium oxide compound and firing, barium titanate particles having an acicular or plate shape extending in the a-axis direction can be obtained. Mixing such particles with a piezoelectric polymer compound such as polyvinylidene fluoride or polyvinyl chloride,
By molding, a part or almost all of the barium titanate particles having an acicular or plate-like shape are oriented in a certain plane or in a certain direction within the piezoelectric polymer compound, and then polarization treatment is performed. It was found that the shoelectric polymer composite material made of this material has a large shoelectric constant compared to a conventional composite material using barium titanate particles that do not exhibit a specific shape. The emissivity of composite materials is explained by introducing the idea of a cavity electric field.

That is, the emissivity d of the composite material is d=q., where d' is the pressure constant of the ceramic. X. G. It is expressed as d'.

Here, q: Volume fraction of ferroelectric ceramic ×: Polarization degree of ferroelectric ceramic G: Coefficient due to cavity electric field
It is.

In order to increase the piezoelectric constant of the composite material, an important factor is to increase the barb G by filling the composite material highly with ceramics having high piezoelectricity and performing sufficient polarization treatment.

G represents how much voltage is applied from the outside of the composite material to the ceramic particles, and is determined by the shape of the ceramic particles, the filling amount, and the dielectric constant of the piezoelectric polymer compound and the ceramic. That is, it is important to fill a high dielectric constant polymer compound with low dielectric constant ceramic particles in order to increase G. The barium titanate particles used in the present invention have an acicular or plate-like shape extending in the a-axis direction, as shown in FIG. 3, unlike conventional barium titanate particles that have an irregular shape. Most of the grain plate surfaces are made up of single crystal grains showing the c-axis direction. It is already well known that the dielectric constant of barium titanate single crystal is different between the a-axis and the c-axis.
It shows a value of about 2900 in the wisteria direction and about 170 in the c-axis direction.
Therefore, when the barium titanate particles used in the present invention are oriented and aligned in the axial direction, the dielectric constant becomes low in the c-axis direction. When producing piezoelectric polymer composite materials, a solution method and a drilling method are known.

The former involves dissolving a piezoelectric polymer compound in an appropriate solvent, mixing ceramic particles into this solvent using a ball mill, and then
This is a method of forming a film into a film by casting. On the other hand, the latter is a method in which a shoelectric polymer compound and ceramic particles are kneaded with a roll and then formed into a sheet by hot press molding.In the former case, barium titanate particles having a specific shape are Due to natural sedimentation within
In the latter, some or almost all of the particles are oriented within a piezoelectric polymer material in a certain plane or in a certain direction as shown in Figure 4. This is a diagram showing the arrangement of particles in a substance, and the c-axis direction is aligned in the thickness direction of the sheet.In other words, it shows that the C-plane is aligned in a constant plane.On the other hand, in the thickness direction of the sheet, the c-axis direction is aligned. This shows that the a-axis is oriented in a certain direction in the vertical direction.The degree of orientation of the particles is greater in the latter case where the pressure treatment is applied.Due to the orientation treatment, only the sheet direction is The c-axis direction of barium titanate particles is aligned,
Since the a-axis direction is aligned in the direction perpendicular to the thickness direction of the sheet, the dielectric constant in the thickness direction of the sheet becomes small. Furthermore, when using conventional barium titanate particles that do not have a specific shape, the particles are disordered in all directions, whereas the composite material according to the present invention has titanium particles in the thickness direction of the sheet. Since the c-axes of the barium acid particles are mostly aligned, they are easily polarized when a DC voltage is applied in the thickness direction of the sheet. Therefore, the piezoelectric polymer composite material according to the present invention can obtain a higher dimensional and piezoelectric constant compared to conventional composite materials. A detailed explanation will be given below based on examples.

Example 1 Potassium carbonate (K2CQ), titanium dioxide (Ti02)
and potassium molybdate (K2Moo4) as mother K2C
After weighing to have a composition of 03-24Ti02-70K2Moo4, the mixture was mixed in a boiler and fired in a platinum rubbo at 110,000 yen for 2 hours and cooled at a cooling rate of 400/min.

This was thoroughly washed with water to completely remove the K2Moo4 component, and then dried.
Two fibers were produced. This fiber was acid-treated with IN hydrochloric acid to produce acicular particles of hydrated titanium dioxide with a size of 5 to 40 m. Next, the hydrous titanium dioxide and barium carbonate were blended in an equimolar ratio, mixed in a ball mill, and fired at 1100 pm for 1 hour. Phase analysis of these particles was performed using X-ray diffraction, observation of the particle shape using an electron microscope, and electron beam diffraction measurements revealed that the particles were acicular or plate-like with a length of 3 to 30 mm, elongated in the a-axis direction. It was confirmed that most of the plate surfaces of barium titanate particles were in the c-axis direction. Next, 20 to 70% by weight of the above-mentioned barium titanate particles were mixed with polyvinyl chloride (PVC) using a hot roll at 20,000 yen, and heated to a thickness of 10 % by weight.
A film of 0 French m was produced.

Electrodes were provided on both sides of this film by gold evaporation, and a DC electric field of 15 V/ga was applied in the thickness direction of the film for 1 hour in 12,000 ℃, and after polarization treatment by slowly cooling it to near room temperature, the piezoelectric constant d,3(egsesu) was measured. The results are shown by the solid line in FIG. Next, for comparison, barium titanate particles (150 to 300 mesh) that do not have a specific shape that have been used in the past were mixed and molded under the same conditions, and then polarized, and the piezoelectric constant d, 3 was measured. The results are shown by the broken line in FIG. As is clear from FIG. 1, the larger the amount of barium titanate particles mixed in, the larger the piezoelectric constant, and the composite material prepared by the method of the present invention has a larger piezoelectric constant than the conventional one. It was confirmed that After molding the composite material according to the present invention and the conventional composite material, X-rays were irradiated in the thickness direction of the sheet and the peak intensity of X-ray diffraction was measured.
The value of 1 (blood 1)/21 (h skin) was extremely large, indicating that the piezoelectric polymer composite material according to the present invention had a considerable number of barium titanate particles aligned in the thickness direction of the sheet. However, 21 (blood 1) indicates the sum of the peak intensities of the (blood 1) plane and the sum of the peak intensities of the 21 (hoo) plane.

Example 2 The acicular particles of hydrous titanium dioxide produced in Example 1 were heat treated at 850 oo for 1 hour. The obtained powder is ×
From the measurement results of line diffraction, electron microscopy, and electron beam diffraction, a
They were anatase-type titanium dioxide acicular particles with a size of 1 to low m that were elongated in the axial direction. The titanium dioxide particles and barium oxide (side 0) were blended and mixed in an equimolar ratio, and then fired at 1100q○ for 2 hours. The obtained powder is
As a result of measurement results of X-ray diffraction and electron beam diffraction and observation of particle shape using an electron microscope, the particle shape has a needle-like or plate-like shape extending in the a-axis direction with a length of 1 to 8 m, and the plate surface It was found that most of the barium titanate particles were oriented in the c-axis direction. Next, in a dimethylformamide solution containing 2% by weight of polyvinylidene fluoride, the aforementioned barium titanate particles were added in an amount of 20 to 7% by weight based on polyvinylidene fluoride.
After mixing in a ball mill for one hour,
Pour it onto a glass plate and evaporate the solvent at 65qo to a thickness of 7
A shoelectric film made of polyvinylidene fluoride-barium titanate with a thickness of 0 mm was produced. This film was subjected to polarization treatment in the same manner as in Example 1, and the piezoelectric constants d, 3 were measured, and the results are shown by the solid line in FIG. For comparison, as in Example 1, conventionally used barium titanate particles that do not exhibit a specific shape were treated under exactly the same conditions, and the piezoelectric constant d,3 was measured. The results are shown in Figure 2. Indicated by the dashed line.
As is clear from FIG. 2, it can be seen that the composite material according to the present invention exhibits a larger piezoelectric constant than the conventional one.
As in Example 1, the composite material according to the present invention and the conventional composite material were subjected to X-ray diffraction measurements after molding, and the results showed that the former had a larger value of 21 (ool)/21 (h skin). It was confirmed that the c-axes of the barium titanate particles were aligned in the thickness direction of the sheet. As is clear from the above results, by mixing barium titanate particles having an acicular or plate-like particle shape extending in the a-axis direction with a piezoelectric polymer compound and molding the mixture, barium titanate particles can be By orienting part or almost all of it in a fixed plane or in a fixed direction within a piezoelectric polymeric material and then polarizing it, it is possible to create a composite material that is made of barium titanate particles that do not have a specific shape, which has been used for a long time. , a shoelectric polymer composite material with a large shoelectric constant can be obtained.

In the examples of the present invention, polyvinylidene fluoride and pinyl chloride were used as piezoelectric polymer compounds, but any piezoelectric polymer compound such as polyvinyl fluoride, polycarbonate, polyvinylidene chloride, nylon, tetron, etc. Needless to say, the effect will be greater when used.

The composite material according to the present invention has excellent processability and moldability, and can be easily formed into a sheet. Furthermore, because it has large electric current characteristics, it can be applied to speakers, microphones, piezoelectric switches, etc., and its industrial value is extremely large.

[Brief explanation of drawings]

Figures 1 and 2 are diagrams showing the relationship between the amount of barium titanate mixed and the Shoelectric constant of the piezoelectric polymer composite material of the present invention in comparison with conventional materials, and Figure 3 is a diagram showing the relationship between the amount of barium titanate mixed and the Shoelectric constant of the piezoelectric polymer composite material of the present invention, and Figure 3 FIG. 4 is a diagram showing the crystal axis direction of barium titanate particles, and FIG. 4 is a diagram showing the arrangement of particles in a piezoelectric polymer material. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. Part or almost all of barium titanate particles having a needle-like or plate-like particle shape are oriented in a certain plane or in a certain direction within a piezoelectric polymer compound. Features of piezoelectric polymer composite material. 2 By mixing and molding barium titanate particles having a needle-like or plate-like particle shape extending in the a-axis direction and a piezoelectric polymer compound, a part or almost all of the barium titanate particles can be made into a piezoelectric polymer compound. 1. A method for producing a piezoelectric polymer composite material, which comprises orienting a molecular compound in a certain plane or in a certain direction, and then subjecting it to polarization treatment. 3. In claim 2, the barium titanate particles have an acicular or plate-like particle shape extending in the a-axis direction obtained by mixing acicular hydrated titanium dioxide particles with a barium compound and firing the mixture. A method for producing a piezoelectric polymer composite material, the method comprising using barium titanate particles having the following properties. 4 In claim 2, barium titanate particles are obtained by mixing a barium compound with a powder consisting of acicular-shaped anatase-type titanium dioxide particles obtained by heat-treating hydrous titanium dioxide acicular particles. A method for producing a piezoelectric polymer composite material, characterized in that barium titanate particles having a needle-like or plate-like particle shape extending in the a-axis direction obtained by firing are used.