JPH069869A - Polymer composite piezoelectric substance and its production - Google Patents

Abstract

PURPOSE:To obtain the a polymer composite piezoelectric substance having stable electric characteristics even under high temperatures by forming a thin film from a solution containing a polyparabanic acid resin and ferroelectric ceramic fine particles by a solvent casting method and subsequently converting the thin film into an electret by a specific method. CONSTITUTION:(A) 90-10vol.% of a polyparabanic acid resin of formula I (R is group of formula II, III, etc.; m is 1-10) and (B) 10-90vol.% of a ferrodielectric ceramic are added to a solvent capable of dissolving the component A to obtain a mixture solution. The solution is formed into a thin film by a solvent cast method and then dried to leave 0.01-10wt.% of the solvent. Finally, the thin film is subjected to the application of an electric field at -10 to 250 deg.C to polarize the film into an electret for providing the objective piezoelectric substance. The component A is preferably obtained from a diisocyanate of formula: OCN- R-NCO and hydrocyanic acid through a compound of formula IV. The component B is preferably fine particles having a diameter of 0.2-44mum which is produced by grinding an inorganic piezoelectric substance such as lead titanate and subsequently subjecting the ground product to a thermal treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer composite piezoelectric body composed of a polymer substance and ferroelectric ceramic fine particles,
In particular, the present invention relates to a piezoelectric polymer having stable properties even at high temperatures.

[0002]

2. Description of the Related Art Piezoelectric materials include inorganic piezoelectric materials such as quartz, Rochelle salt, lead zirconate titanate (PZT), and natural polymers such as cellulose and collagen, polyvinylidene fluoride, polyvinyl chloride and the like. There are organic piezoelectric materials such as polymers. Of these, the inorganic piezoelectric material is difficult to mold, and thus it is difficult to obtain a thin piezoelectric material or a flexible piezoelectric material. On the other hand, the organic piezoelectric material has problems such as anisotropy in piezoelectricity and small piezoelectricity even if a flexible piezoelectric body is obtained.

As an example of improving these problems, for example, ferroelectric ceramic fine particles described in JP-A Nos. 50-159185 and 54-5598 are used as polyacetals.
2. Description of the Related Art Polymer composite piezoelectric materials that are dispersed and mixed in a polymer material such as a fluororesin are known. This polymer composite piezoelectric body has characteristics that it has greater piezoelectricity than organic piezoelectric bodies and that there is no piezoelectric anisotropy.

[0004]

However, this conventional polymer composite piezoelectric body is limited in its application range when it is used in an environment of 80 ° C. or higher for a long period of time, because piezoelectricity deterioration such as depolarization occurs. There's a problem. The purpose of the present invention is to
It is an object of the present invention to provide a polymer composite piezoelectric body which is flexible, easy to mold and can be used for a long period of time even at a high temperature of about 150 ° C., and a method for producing the same.

[0005]

The first object of the present invention is to provide a polymer composite piezoelectric material which comprises the following components (a) and (b) and which is stable even at high temperatures by being electretized. is there. (A) General formula

[0006]

[Chemical 2]

Polyparabanic acid resin represented by
volume%. (B) Ferroelectric ceramic fine particles, 10 to 90% by volume. Further, according to the present invention, (A) a step of adding 90 to 10% by volume of the polyparabanic acid resin and 10 to 90% by volume of the ferroelectric ceramics to the solvent in which the polyparabanic acid resin is soluble to form a mixed solution, ) A step of forming the mixed solution into a thin film by a solvent casting method, and (C) the thin film containing a solvent of 0.
01 to 10% by weight of the step of preparing a state that remains,
(D) A method for producing a polymer composite piezoelectric body is obtained, which comprises a step of applying a predetermined electric field to polarize the thin film after preparation at a temperature of -10 ° C to 250 ° C.

[0008]

EXAMPLES Polyparabanic acid (PP used in the present invention
A) is produced from diisocyanate and hydrocyanic acid by the following formula.

[0009]

[Chemical 3]

As -R-,

[0011]

[Chemical 4]

Is used, preferably

[0013]

[Chemical 5]

Is used. In order to manufacture the polymer composite piezoelectric material of the present invention, polyparabanic acid is added in an amount of 10 to 90 with respect to the contents of the polyparabanic acid and the ferroelectric ceramic fine particles.
Use by volume%. As the ferroelectric ceramic fine particles,
Inorganic piezoelectric materials such as lead zirconate titanate (PZT), lead titanate, and barium titanate are crushed and heat-treated to use fine particles having a diameter of 0.2 to 44 μm. The amount of the ceramic fine particles is 10 to 90% by volume.

(Mixing) Polyparabanic acid and ferroelectric ceramic fine particles are mixed by dissolving polyparabanic acid in a solvent to form a solution, and adding the ferroelectric ceramic fine particles to this solution, various mixers, ball mills, mixing rolls and the like are commonly used. It can be performed using a mixing method.

As a solvent for dissolving polyparabanic acid,
Dimethylformamide, dimethylacetamide, N-methylpyrrolidone, dioxane, gammabutyrolactone,
Cyclohexanone or the like can be used. Preference is given to using dimethylformamide.

(Molding) As a molding method, a solvent casting method can be used. At this time, the solution viscosity is adjusted to 10 to 5000 poises, preferably 250 to 2500 poises in order to prevent phase separation due to the difference in specific gravity between the polyparabanic acid and the ferroelectric ceramic fine particles and obtain a uniform molded body. The molding temperature can be room temperature, and the solution can be cast on a cast substrate (glass, Teflon substrate, etc.), and the film thickness can be adjusted to 30 to 200 μm using, for example, a Baker applicator. After the solvent casting, the molded body is dried on the substrate. Further, the residual amount of the solvent can be arbitrarily changed by adjusting the standing time in a vacuum dryer at an arbitrary temperature (room temperature to 100 ° C.), for example.

(Electretization) In order to impart piezoelectricity to the above-mentioned molded body, a DC electric field or a synergistic DC electric field is applied from the front and back of the molded body for a certain time while the molded body is heated to a predetermined temperature. After that, thermal electretization is performed by cooling to room temperature and removing the electric field.

When the molded body is completely dried, thermal electretization causes the glass transition point (290) of polyparabanic acid.
It is possible at temperatures near ℃), but due to thermal degradation of the polymer, 250
Below 0 ° C, there is a problem that sufficient piezoelectricity cannot be obtained.

On the other hand, if 0.01 to 10% by weight, preferably 0.1 to 2% by weight, of the solvent remains, the molded product becomes electrically conductive, so that it is -10 to 250 ° C, preferably 20. Thermal electret can be easily formed in a temperature range of up to 200 ° C. In order to leave the solvent in the molded body, the solvent used when the molded body is produced by the solvent casting method may be left, or the dried molded body may be immersed in the solvent to impregnate the solvent. Since the remaining solvent can be easily removed by drying under reduced pressure after thermal electretization, electretization is possible without deteriorating electrical characteristics such as volume resistivity.

The electric field is applied by using electrodes in which a metal foil, a conductive resin, and a conductive paste are adhered to the front and back surfaces of the molded body. The strength of the electric field is generally 10 kV / cm to the extent that dielectric breakdown of the molded body does not occur, preferably 50 to 300.
Set to kV / cm. The application time of the electric field is not particularly limited, but is preferably 5 minutes or more.

The glass transition temperature of polyparabanic acid is 290 ° C.
Since it is an amorphous polymer, it has stable physical properties (dielectricity, volume resistivity, heat resistance, etc.) below the glass transition point. Therefore, even if a polymer composite piezoelectric material with ferroelectric ceramic particles is formed, the electrical characteristics (piezoelectric property, dielectric property, volume resistivity, etc.) are stable up to a high temperature. Also, because it has excellent chemical resistance, especially acid resistance, unlike amorphous polymer polyether sulfone, it is a ferroelectric ceramic that becomes a solid acid due to the presence of water (for example, lead zirconate titanate, lead titanate, titanate). Even when coexisting with barium), the polymer does not decompose and a stable polymer composite can be formed.

(Experimental Example) Next, an experimental example of the present invention will be described. In the examples, the elastic modulus (E) and the piezoelectric modulus (d ₃₁ ) were measured at 135 Hz, and the dielectric constant was measured at 100 Hz. The viscosity was measured using an E-type viscometer (manufactured by Tokyo Keiki Co., Ltd.).

Experimental Example 1 (1) Polyparabanic acid represented by the formula (I) (PPA:
Specific gravity 1.33) to dimethylformamide (DMF) 2
Lead titanate zirconate (PZT: specific gravity 7.9) 74.5 in 25.95 g of DMF solution of PPA dissolved 1% by weight
After adding 5 g and further adding DMF 4% by weight (4.0 g) and stirring well, the mixture was well kneaded and mixed with a mixing roll to prepare a uniform sample solution. Here, the volume fraction of PPA and PZT is 30/70. The viscosity of the sample solution at this time is
It was about 1000 poise. (2) After defoaming the obtained sample solution, a film coater (PI-1210 manufactured by Tester Sankyo Co., Ltd.) is used to form a composite film of 10 cm × 30 cm × 130 μm, and the composite film is dried in a dryer at 40 ° C. Dried for hours. (3) The obtained composite membrane was compressed to about 100 μm at room temperature using a compression press and filled with the void phase generated by desolvation. The residual solvent amount at this time is about 1% by weight by thermogravimetric analysis.
Met. (4) Tin foil was adhered to the front and back surfaces of the obtained composite film to form electrodes, and electrodes were placed between the electrodes in an oven heated to 100 ° C.
A direct current electric field of 100 V (100 kV / cm) was applied for 1.5 hours, and after cooling to room temperature, the electric field was removed to form a thermo electret. (5) Heat-electretized composite film
It was dried under reduced pressure for an hour and desolvated. (6) When the performance of the obtained polymer composite piezoelectric material was measured, the following values were obtained.

Elastic Modulus (E) 4.5 × 10 ¹⁰ dyn / cm
² Volume resistivity (Rv) 1 × 10 ¹⁵ Ω · cm Dielectric constant (ε) 65 Piezoelectric constant (d ₃₁ ) 5 × 10 ^-12 C / N

Experimental Example 2 In Example 1, a composite piezoelectric material was manufactured by changing only the temperature at which the material was thermally electretized. Table 1 shows the electrical characteristics of the obtained piezoelectric body.

[0027]

[Table 1]

Experimental Example 3 In Example 1, a composite piezoelectric body was manufactured by changing only the composition ratio of PPA resin and PZT fine particles. Table 2 shows the electrical characteristics of the obtained piezoelectric body.

[0029]

[Table 2]

Experimental Example 4 In Example 1, a composite piezoelectric material was manufactured by changing only the time of thermal electretization. Table 3 shows the electrical characteristics of the obtained piezoelectric body.

[0031]

[Table 3]

Experimental Example 5 In Example 1, a composite piezoelectric material was manufactured by changing only the electric field for thermal electretization. Table 4 shows the electrical characteristics of the obtained piezoelectric body.

[0033]

[Table 4]

Experimental Example 6 The same method as in Example 1 was repeated except that the amount of residual solvent in the composite film was adjusted to 0.01 to 10% by weight by changing the drying time in the step (2) of Example 1. A composite piezoelectric body was manufactured. Table 5 shows the electrical characteristics of the obtained piezoelectric body.

[0035]

[Table 5]

Experimental Example 7 The composite film prepared in steps (1) to (3) of Example 1 was
A composite piezoelectric film was manufactured by drying under reduced pressure at 60 ° C. for 12 hours to completely remove the solvent and changing the temperature for thermal electretization. Table 6 shows the electrical characteristics of the obtained piezoelectric body. It can be seen that in the case of a composite film containing no solvent, orientation polarization does not proceed sufficiently even if it is electretized at 250 ° C. or lower, and large piezoelectricity is not exhibited.

[0037]

[Table 6]

Experimental Example 8 The composite membrane prepared in steps (1) to (3) of Example 1 was dried under reduced pressure at 160 ° C. for 12 hours before the step (4) of Example 1 to completely remove the solvent and dry it. A composite piezoelectric material was manufactured by the same method as in Example 1 except that the composite film was immersed in methanol for 1 minute to impregnate it with methanol. The electrical characteristics of the obtained piezoelectric body are as follows. It can be seen that if the solvent is allowed to exist again in the composite film after the removal of the medium, the orientation polarization is sufficiently advanced as in Example 1.

Elastic Modulus (E) 4.2 × 10 ¹⁰ dyn / cm
² Volume resistivity (Rv) 1 × 10 ¹⁵ Ω · cm Dielectric constant (ε) 63 Piezoelectric constant (d ₃₁ ) 4.1 × 10 ⁻¹² C / N

Experimental Example 9 A composite piezoelectric material was manufactured by the same method as in Example 1 except that the viscosity of the sample solution was changed by changing the amount of solvent in Example 1. Table 7 shows the electrical characteristics of the obtained piezoelectric body. When the solution viscosity is 10 poise or less, a composite film can be produced, but the PZT fine particles settle out during the film formation and undergo phase separation, which is not practical.

[0041]

[Table 7]

Experimental Example 10 A composite piezoelectric material was manufactured by the same method as in Example 1, stored in an oven heated to 150 ° C. after nitrogen substitution, and the result of measuring the piezoelectric constant at room temperature is shown in FIG. After the unstable part of orientation polarization decays immediately after storage, it stabilizes after 30 hours and reaches 4000.
It can be seen that 85% of the initial value is maintained even after a lapse of time.

[0043]

As described above, according to the present invention, it is possible to obtain a polymer composite piezoelectric material which is flexible, easy to mold and can be used for a long time even at high temperature, and a method for producing the same. .

[Brief description of drawings]

FIG. 1 is a graph showing the measurement results of Experimental Example 10.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location H01L 41/26 // C08G 73/06 NTM 9285-4J (72) Inventor Mariko Kishida Inashiki-gun, Ibaraki Prefecture 8-3-1 Chuo, Ami-cho Mitsubishi Petrochemical Co., Ltd. Tsukuba Research Institute (72) Inventor Eisuke Yasukawa 8-3-1 Chuo, Ami-cho, Inashiki-gun, Ibaraki Mitsubishi Petrochemical Co., Ltd. Tsukuba Research Institute (72 ) Inventor Iwao Seo 8-3-1 Chuo, Ami-machi, Inashiki-gun, Ibaraki Mitsubishi Petrochemical Co., Ltd. Tsukuba Research Institute

Claims (2)

[Claims] 1. A method comprising the following components (a) and (b):
In addition, a polymer composite piezoelectric body formed into an electret. (A) General formula: Polyparabanic acid resin shown, 90-10% by volume. (B) Ferroelectric ceramic fine particles, 10 to 90% by volume. 2. A solvent in which the (A) polyparabanic acid resin is soluble,
A step of adding 90 to 10% by volume of polyparabanic acid resin and 10 to 90% by volume of ferroelectric ceramics to form a mixed solution; (B) a step of thinning the mixed solution by a solvent casting method; (C) The thin film contains 0.01-1 solvent.
2. The method according to claim 1, comprising a step of preparing a state in which 0 wt% remains, and a step of (D) applying the predetermined electric field to polarize the thin film after preparation at a temperature of -10 ° C to 250 ° C. Method for manufacturing molecular composite piezoelectric body.