JPS5946433B2 - Method for manufacturing piezoelectric polymer composite - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a flexible piezoelectric polymer composite.

Conventionally, crystals such as quartz, Rothsiel's salt, and ceramics such as barium titanate are well known as piezoelectric substances.

Although these materials all have great piezoelectricity, they are hard and difficult to process, making it extremely difficult to obtain thin film piezoelectric bodies or flexible piezoelectric bodies. On the other hand, although it has been confirmed that uniaxially stretched membranes of amino acid polymers such as polybenzyl glutamate and organic materials such as polyvinyl chloride, polyamide, and collagen can maintain piezoelectricity, the piezoelectricity of all of them is small and the piezoelectric effect Even in polyvinylidene fluoride, which is said to have the largest value, the piezoelectric constant of longitudinal vibration is only 6.7 x 10-12 m/liter.

Furthermore, in the case where piezoelectric fine particles are composited with a polymeric material and then polarization is performed by applying a DC voltage at an appropriate temperature, most of the electric field during polarization is distributed to the polymeric material, and the ferroelectric fine particles are I can't get enough orientation. In other words, it could not be said that the effect of improving piezoelectricity by adding piezoelectric fine particles was sufficiently exhibited. This fact becomes more noticeable as the amount of ferroelectric fine particles compounded into the thermoplastic polymer increases. On the other hand, when selecting a thermoplastic polymer material, it is necessary to select a polymer material with a large dielectric constant so that the electric field during polarization can distribute the electric field to the piezoelectric particles, and the ferroelectric particles can be sufficiently oriented. In practice, polyvinylidene fluoride was often used. In view of the above-mentioned drawbacks, the present invention aims to provide a manufacturing method that can easily be formed into a thin film and that can obtain a piezoelectric polymer composite having high piezoelectricity.

That is, in the present invention, a composite consisting of a thermoplastic polymer material containing piezoelectric inorganic fine particles that have been polarized and oriented in advance is stretched, and then a polarization operation is further performed to obtain large piezoelectricity. It is characterized by

By subjecting the piezoelectric inorganic fine particles that have been polarized and oriented in advance to a composite with a thermoplastic polymer material, and then adjusting the orientation direction under a DC electric field after stretching, piezoelectricity that depends on the piezoelectric inorganic fine particles can be achieved. is greatly improved.

That is, a piezoelectric constant several times larger than that of the conventionally known composite type was obtained. As the thermoplastic polymer material, it is particularly preferable to use polyvinylidene fluoride, polyvinyl chloride, polyvinylidene chloride, fluorine-based plastics, polyacrylonitrile, and nylon 11 (trade name), and as the piezoelectric inorganic material, strong Dielectric piezoelectric materials are preferred, and in addition to PbTiO3-PbZrO3 systems, Rothsiel salt, quartz, etc. can also be used.

Furthermore, as a method for obtaining polarized piezoelectric inorganic fine particles, a ceramic molded body using a polymeric binder was
Main firing is carried out at a temperature of 00'C to 1400℃, and the obtained solid is polarized or sliced to an arbitrary thickness, wrapped, and then electrodes are provided on both surfaces for polarization and pulverization. (You may remove it by etching etc.)
. Similar to No. 21, the main fired solid is crushed and polarized.

3 Ceramic powder is fired and polarized.

Further, there are the following methods for combining a thermoplastic polymer material and piezoelectric inorganic fine particles.

A thermoplastic polymer material and pre-polarized piezoelectric inorganic fine particles are mixed and composited using a roll plastograph or the like at a temperature of 1 softening point or higher, and then formed into a film or sheet.

2. After dissolving the thermoplastic polymer material in a suitable solvent, it is thoroughly mixed with pre-polarized piezoelectric inorganic fine particles using a ball mill, etc., and then formed into a sheet or film using a solution casting method.

As for the ratio of the thermoplastic polymer material to the piezoelectric inorganic fine particles, it is possible to mix the piezoelectric inorganic fine particles in an amount of 10 to 97% by weight based on the thermoplastic polymer material. It is preferable to use a material containing 30 to 92% by weight of piezoelectric inorganic fine particles depending on conditions such as mechanical strength, magnitude of induced voltage, and quality of stretching. Further, there is a problem when compounding pre-polarized piezoelectric fine particles with a thermoplastic polymer material: 1. The orientation direction of the pre-polarized piezoelectric fine particles becomes random.

In order to apply a sufficiently high electric field to the film or sheet to align the two orientation directions, the film or sheet must have a sufficient withstand voltage.

However, the present inventors have solved the problems 1 and 2 above by performing polarization treatment in insulating oil or inert gas, and have obtained a composite film or sheet that retains extremely high piezoelectricity. . The size of the piezoelectric inorganic fine particles is fine as long as it is 100 meshes or more, and fine particles of 350 meshes or more are also effective, but preferably the shape of the fine particles is spherical, and when compounding, two or more fine particles are used. It is desirable to have a particle size of .

It was confirmed that all of the following stretching methods were sufficiently effective.

1 Roll stretching at room temperature.

If stretching is difficult, warm the rolls to the lowest possible temperature and stretch. 2 Stretching by mechanical tension.

3. After stretching the film formed by the solution casting method in the same manner as in 1 or 2 above, with the solvent still not completely removed,
Remove solvent completely.

After stretching in this manner, suitable electrodes are attached to both sides of the film or sheet, and a polarization operation is applied to the film or sheet in an insulating oil or inert gas by applying a DC voltage. In this case too, the temperature is 90-130
It is more effective to keep it at around ℃. In addition, as mentioned before, the DC applied voltage reorients some of the piezoelectric fine particles that are oriented in random directions and makes them align in the same direction, so the higher the voltage, the better. The more applied, the larger the piezoelectric voltage becomes. Additionally, a plasticizer can be added as necessary to increase the stretchability and mechanical strength of the product, but if it does not significantly reduce the insulation resistance, the electrodes on the pre-polarized ceramic plate can be removed by etching, etc. Even if it is directly pulverized and composited without cutting, it does not have a large effect on the piezoelectric voltage.

Examples of the present invention will be shown below.

Example 1 Pre-polarized (D3l=1.2×10-1
0 m/v) lead zirconate titanate (hereinafter referred to as PZT).

) Porcelain was milled using a stamp mill and a ball mill to reduce the average particle size to 2μ.
, 5μ, and 10μ to obtain piezoelectric inorganic fine particles. These piezoelectric inorganic fine particles (2μ:5μ:10μ
NiJ Me F2:1) 100gr. and polyvinylidene fluoride powder 100g. The mixture is kneaded with heated rolls at 180 to 200°C, and then formed into a sheet with a thickness of about 200μ by pressing at the same temperature. The sheet is then stretched twice between rolls at room temperature. Electrodes were provided on both sides of this sheet by vacuum deposition, sputtering, plating, printing, etc., and a direct current electric field of 500 K'I/Cm was applied for 24 hours in silicone oil at 120° C. to obtain a piezoelectric body. And from this the width is 5 and the length is 4
Two samples were cut out and piezoelectric pressure was extracted from both surfaces using aluminum foil. In addition, as the piezoelectric inorganic fine particles, four types of PZT-based porcelain piezoelectric materials with different piezoelectric constants (D3l = 1.2
Mowing 0-10rn/V, l. O×10-10m/V, O.
7 x 10-10, 0.4 x 10-105 - the same material with different polarization conditions and piezoelectric constant) was measured, and the piezoelectric constant (D3l) was measured using the conventional method (thermoplastic Table 1 also shows the cases where the above seven piezoelectric fine particles whose polymeric material was not subjected to polarization treatment in advance were used. Example 2 Similar to Example 1, pre-polarized PZT porcelain (0.4
×10-10 town, 0.7×10-10 exposure, 1.0×1
0-10 m/m/cm) with an average particle size of 2μ, 5μ, and 10μ using a stamp mill and a ball mill.
It was crushed into different types to produce piezoelectric fine particles.

This piezoelectric fine particle (2μ:5μ:10μ=7:2:1)
100 gr. and nylon 11 powder 100g. **1
The mixture is kneaded with heated rolls at 50 to 170°C, and then formed into a sheet with a thickness of about 200 μm by pressing at the same temperature. Next, it was stretched to about twice the size using a stretching roll, and after attaching electrodes, a DC electric field of 500 KV was applied for 24 hours in silicone oil at 120° C. to obtain a piezoelectric body. Thereafter, the piezoelectric constant in the longitudinal direction was measured in the same manner as in Example 1. The results are shown in Table 2. As a result of the above, the piezoelectric polymer composite produced by the method of the present invention exhibits excellent piezoelectric constant and also has flexibility, so that it is extremely effective in the form of a film as an electromechanical transducer in the audio band.

Claims (1)

[Claims] 1. A step of stretching a film-like or sheet-like composite made of a thermoplastic polymer material containing piezoelectric inorganic fine powder that has been polarized in advance, and applying a DC voltage to the stretched composite to polarize it. 1. A method for producing a piezoelectric polymer composite, comprising a step of performing a treatment.