JPS6125229B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to piezoelectric polymer composite materials. Generally, attempts to obtain this type of piezoelectric material by mixing a polymer substance and ferroelectric porcelain powder are known;
After producing ferroelectric ceramics such as BaTiO ₃ , PdTiO ₃ or PbZrO ₃ -PbTiO ₃ solid solution through solid-state reaction under heating, or synthesizing single crystals such as potassium sodium niobate (DSN), it is exclusively produced by ball milling. The particles were adjusted to the required particle size by being pulverized using a pulverizer such as a vibrating mill. However, when ferroelectric porcelain powder that has undergone such a crushing process is combined with a polymeric substance, the piezoelectric properties are significantly different from those expected from the porcelain composition itself, and only low performance is obtained. Due to the drawbacks associated with the formulation, such as the material being brittle and easily torn, the material becoming less flexible, making it difficult to mold, and the molded product being heavy and costly, it has remained virtually unpractical to date. It has not reached the level of The inventors conducted a fundamental investigation into the cause of the above-mentioned performance deterioration that occurred when using the above-mentioned porcelain powder, and as a result, they obtained the following knowledge. First, structural destruction occurs in microcrystals during the crushing process performed after solid phase reaction or single crystal synthesis, resulting in the formation of countless domains or irregular phases. Next, multi-regionalization within microcrystals means that when the irregular phase undergoes a polarization treatment after undergoing a compounding process with a polymeric substance, the effective electric field acting on the porcelain powder is affected by the polymeric substance. Coupled with the fact that it is unavoidable that the ratio to the dielectric constant decreases significantly from tens to hundreds of times, even if polarization is performed at a high voltage close to the withstand voltage of the composite material, the above-mentioned When the electric field is lowered to 1, the polarization is almost no longer aligned in the direction of the electric field, and therefore sufficient piezoelectricity cannot be achieved. There is almost no point in mixing porcelain powder or single crystal with polymeric substances in this way. As a result of numerous experiments and research, the inventors discovered that a ferroelectric porcelain powder consisting of single-domain microcrystals with uniform grain size could be obtained as shown below, and that In contrast, ferromagnetic powder, which is made up of one-domain microcrystals, can be combined with a specific amount of polymeric material to produce piezoelectric polymer composites with unparalleled and outstanding performance without any difficulties in the manufacturing process. We have discovered that this can be achieved without the need for Now, ferroelectric porcelain powder consisting of single-domain microcrystals with uniform particle size can only be obtained through the following treatment. (1) Prepare and mix raw material powders corresponding to the desired ferroelectric ceramic composition. (2) Synthesizing the above blended raw material powder by heating solid phase reaction or sintering treatment. (3) Grind the composite to the desired particle size. (4) Next, the pulverized material is heated and annealed. At this time, it is desirable to carry out the process in the atmosphere or in an atmosphere with an oxygen concentration higher than that. (5) Furthermore, the processed material is subjected to chemical etching treatment. During the above treatment step (3), as mentioned above, structural destruction occurs in the microcrystal, resulting in the generation of countless domains and irregular phases. This is improved by applying heat annealing treatment in 4), and at the same time, the effect of rounding the crystal grains is produced by heat, and furthermore, by applying the etching treatment in (5), the grain size becomes uniform and roundness is achieved. It was found that single-domain microcrystals were obtained. The reason for this is that etching preferentially acts on grain boundaries and removes impurities, foreign matter, crystal lattice defects, amorphous parts, etc. that are present in large quantities at grain boundaries, and also removes fused secondary particles into single particles. This is because it dissociates and decomposes into In other words, impurities that inevitably enter raw materials or during processes such as pulverization are relatively easy to precipitate at grain boundaries, so they can be removed advantageously, and the etching action can round the crystal surface and further improve the ultrafine crystal grains. It also has the advantage of dissolving and disappearing. Note that the effect of etching will be further enhanced if light mechanical crushing, such as submerged stirring, is used in combination. If the temperature is raised further, for example in a low boiling state, the time can be significantly shortened. In any case, the target impurities, irregular layers, amorphous layers, and ultrafine particles should only be dissolved and removed, and the elution of further crystal layers should be kept to a minimum, and appropriate conditions should be maintained to avoid deterioration of piezoelectricity. It is necessary to do so. Of course, strictly speaking from the viewpoint of physical properties theory, the powder obtained in the above manner does not completely become single-domain microcrystals, but may contain impurities, structural irregularities (lattice defects, layer defects, etc.). ), or due to deviations from the stoichiometric ratio, non-uniform composition, or even external factors (heat, stress), etc., some domain formation is observed, and it is impossible to avoid this due to the current level of science and technology. Although it is a self-evident fact in the above-mentioned etching process after heat annealing, the domains generated within the crystal that can be seen by stirring or slight pulverization are caused by alignment in the direction of the electric field due to voltage application during polarization. The inventors have discovered that the powdered product obtained in this way exhibits unidirectional characteristics without being a factor that hinders orientation to electric fields. On the other hand, single crystals and porcelain that are powdered by conventional pulverization after heating synthesis by conventional conventional means cause structural destruction of the crystal, resulting in countless multi-regionalization and further formation. Since these have become irregular and almost no longer aligned in the electric field direction, they are distinguished from these multi-domain microcrystals, and even if they are called single-domain microcrystals, they are not ideal. This does not mean something that cannot be manufactured industrially in real life. The ferroelectric porcelain powder consisting essentially of single-domain crystals that has gone through the above processing steps is mixed with various polymeric substances, formed into any shape such as a film or sheet, and cross-linked or rubber-based. , polarization is performed through vulcanization treatment. Here, even if the effective electric field becomes extremely low, from several tens to several hundred times lower than the dielectric constant of the polymer material, the grain size is made up of single-domain microcrystals with uniform grain size, so the electric field It was confirmed that they were easily assembled and exhibited particularly high ferroelectric and piezoelectric properties. In addition, the powder obtained in this way has a rounded shape of each particle due to heat annealing and chemical etching, so it is compatible with polymers, has no vacuoles, is dense, and has the ability to dissolve ultrafine particles. It has become possible to obtain high-density, high-performance composite materials that are easy to process due to their high plasticity and fluidity, and are even as thin as 15 μm. Since it does not have a fracture surface like a sharp cutting edge or a sharp corner, its mechanical strength is greatly improved, and it can be used as a mechanical and electrical transducer without mechanical damage even when subjected to impact force or tensile stress. This material has also been made into a piezoelectric composite material that can be used in practical applications. Thus, by combining ferroelectric porcelain powder consisting of single-domain microcrystals with a polymeric substance, it can be used in the following industrial fields. The ferroelectric ceramic powder has excellent orientation in the polarization direction and is unidirectional, and the composite material has good processability, making it ideal for biological transducers that require flexibility that is compatible with the human body. Ferroelectric porcelain is suitable for devices that require higher piezoelectric performance even if it lacks flexibility, such as keyboard switches that have a large number of switches integrated on a piezoelectric sheet. A product containing a high proportion of powder is suitable. In this way, it is possible to provide composite piezoelectric materials with mechanical, electrical, and physical properties that suit a wide range of applications, depending on the blending ratio of porcelain powder and polymeric substances, and the selection of polymeric substances. It can be expected to be applied to a wide range of fields in the future, such as electroacoustic conversion and pyroelectric materials. In addition, in known sheets using porcelain powder that cannot avoid multi-regionalization due to conventional crushing, the polarization is severely inhibited as described above, so a high proportion of porcelain powder has to be used in order to meet the required performance. Because of this, the mixed sheet with the polymeric material was hard, brittle, and easily torn at each stage of productization, and could not be put to practical use.However, in this invention, such a high blending ratio is not necessarily required. Since the flexibility of the polymeric material itself is advantageously maintained and a sufficiently high degree of piezoelectric performance is achieved despite this,
This was the first time that a practical application for a piezoelectric polymer composite material that had both characteristics was established. The present invention can be suitably carried out in the following single-component systems, multi-component systems of ferroelectric ceramics having various crystal structures as shown below, as well as those obtained by partial substitution and addition modification of these basic compositions. 1 Perovskite structure (1) Barium titanate and solid solutions around it, such as BaTiO ₃ , (Ba, Pb, Ca)TiO ₃
... etc. (2) Lead titanate and solid solutions centered on it, such as (Pb, La)TiO ₃ , PbTiO ₃ −BiFeO ₃
...etc. (3) Lead zirconate titanate and solid solutions based on it, such as PbZrO ₃ −PbTiO ₃ ,
PbZrO ₃ −PbSmO ₃ −PbTiO ₃ ... etc. (4) Three-component porcelain consisting of a solid solution of lead zirconate titanate and a third component such as a, b and c below, a General formula A ²⁺ (B1/ For example, Pb(Ni1/3−Nb2/3) expressed as 3 ²⁺ −B2/3 ⁵⁺ )O ₃
O ₃ , Pb (Zn1/3−Nb2/3) O ₃ , Pb (Co1/3
−Nb2/3)O ₃ , Pb(Mg1/3−Nb2/3)O ₃ …
...etc. b Expressed by the general formula A ²⁺ (B1/2 ²⁺ −B1/2 ⁶⁺ )O ₃ For example, Pb(Ni1/2−W1/2)
O ₃ , Pb(Co1/2−W1/2)O ₃ ...etc. c Expressed by the general formula A ²⁺ (B1/2 ³⁺ −B1/2 ⁵⁺ )O ₃ For example, Pb(Fe1/2−Nb1 /2)
O ₃ , Pb (Sb1/2−Nb1/2) O ₃ , Pb (Y1/2
-Nb1/2)O ₃ ... etc. (5) Solid solution centered on NaNbO ₃ e.g.
_NaNbO3 , (Na-K) _NbO3 , Na(Ta-Nb)
O ₃ ... etc. 2 Tungsten bronze structure For example, PbNb ₂ O ₆ , PbNb ₂ O ₆ −PbTa ₂ O ₆ ,
PbNb ₂ O ₆ −BaNb ₂ O ₆ ... etc. 3 Bismuth layered structure For example, Bi ₄ Ti ₃ O ₁₂ , Bi ₄ PbTi ₄ O ₁₅ ,
Bi ₄ Sr ₂ Ti ₅ O ₁₈ ... etc. 4 Others LiNbO ₃ , LiTaO ₃ ... etc. 5 Each of the above component systems is the basic composition, and a part of Pb is replaced with an alkaline earth metal 6 Each of the above component systems (including PbTiO ₃ ) as a basic composition, and the following and one or more selected from each group are added as subcomponents,
Metamorphosed () Nb ₂ O ₅ , Ta ₂ O ₅ , La ₂ O ₃ , Sb ₂ O ₅ ,
Sb ₂ O ₃ , Bi ₂ O ₃ , WO ₃ etc. () MgO, Fe ₂ O ₃ , Sc ₂ O ₃ , K ₂ O etc. () Cr ₂ O ₃ , U ₂ O ₃ , MnO ₂ etc. These various ferroelectrics The excellent ferroelectricity, piezoelectricity, and pyroelectricity inherent to each composition can be selected and utilized by changing the basic composition of the porcelain, and by substituting or adding subcomponents. At the same time, it is also possible to control the particle size, lower the coercive electric field to further improve electric field orientation, or conversely increase the coercive electric field to create a composite piezoelectric material that is resistant to static loads, and to stabilize changes over time. This makes it possible to obtain a composite piezoelectric material with width-oriented characteristics suitable for the intended use. Next, in the present invention, the polymeric substance that can be composited with the above-mentioned ferroelectric porcelain, especially the porcelain powder consisting of virtually single-domain microcrystals, includes various rubbers, namely natural, artificial, synthetic, and recycled rubbers. or blend rubbers thereof, especially fluorine rubber and chloroprene, and thermoplastic resins such as polyvinylidene fluoride (PVDF), acrylonitrile-butadiene-styrene copolymer (ABS),
Vinyl chloride (PVC), polyvinyl fluoride (PVF)
etc. The etching solution can be general acids,
An alkaline solution may be used, but care must be taken to only remove the desired irregular layer or amorphous layer, and to elute the Pb component of the crystalline layer to a point where the piezoelectricity is not impaired. Therefore, the lighter the concentration, the easier it is to process, but it takes a long time in a stationary state. However, by raising the temperature, for example, etching while boiling, or by adding stirring or slight pulverization even at room temperature, the time can be greatly shortened, and the etching time can be greatly reduced due to friction and abrasion between the particles. There is an advantage that the corners are further reduced and single crystal grains with a more rounded appearance can be obtained. Next, several examples of standard chemical etching treatment conditions are specifically shown in Table 1 below.

[Table] If the temperature is raised, the processing time can be further shortened. The above etching process is performed using ferroelectric porcelain powder.
It is preferable to use 100g of etching solution per 100g and perform the process under the conditions described above. Examples of the present invention will be described below. Synthesis of ferromagnetic porcelain Commercially available PbO and WO ₃ with purity above 99%, 98.5%
Using the above ZrO ₂ and TiO ₂ of 98% or more _, blend it so that it has a composition of Pb (Ti _{0.5 −} Zr _0.5 ) O ₃ + 1% by weight WO ₃ and weigh out 2.5 kg. The mixture was then dry mixed in a vibrating mill for 5 hours. At this time, the inner wall of the vibrating mill is lined with urethane resin,
Alumina boulders were used to prevent impurities from entering. This mixed powder was packed in a high alumina crucible and PbO
The mixture was maintained at 730° C. for 4 hours in an atmosphere of 100° C., and Pb(Ti _{0.5 −Zr 0.5} )O ₃ +1% by weight WO ₃ was synthesized by solid phase _reaction . Grinding process Add acetone to 200g of powder collected from this, and use a 2-volume alumina ball mill to crush 300g of powder.
milled for 8 hours with alumina boulder of 100 g. (Powder (i)) Annealing After drying the powder i obtained by this pulverization, coarse particles are removed using a 60-mesh sieve. Heat annealing treatment was performed at 950°C for 15 minutes each time. Etching process Next, prepare a diluted solution of reagent-grade glacial acetic acid and water at a volume ratio of 1:1 as an etching solution.
A 300 ml beaker was charged with a volume of 100 ml of the heat-annealed powder, and then the above etching solution was added to make a total of 200 ml, and each of the beakers was subjected to the etching treatment shown below. First, at 950℃, 10/min of O ² (O ₂ concentration 38%)
Powders (a) to (e) were supplied and annealed twice and the etching conditions were changed as follows; Powder (f) was the same as powder (b) but the annealing conditions were changed; and (g) was obtained. (a) 8 hours of etching treatment with 8 hours of stirring using a magnetic stirrer (b) 8 hours of stirring followed by 16 hours of standing for a total of 24 hours
Time etching treatment (c) 8 hours of stirring followed by 40 hours of standing for a total of 48 hours
Time etching treatment (d) Etching treatment for a total of 96 hours, including stirring for 8 hours and then standing for 88 hours. (e) Etching treatment including mechanical crushing. (e) After the above annealing treatment on a 500 ml resin pharmaceutical bottle Add 100g of powder and 150g of alumina cobbles of 18mmφ, inject the etching solution so that the total volume is 300ml, seal it, and apply it to a rotary machine at 100rpm for 3 hours of etching treatment (f) Oxygen is added at 800℃ for 2 hours. /Supplied into the blast furnace ( _C2 concentration
27%) and annealed powder is subjected to the same etching treatment as powder (b) (g) Powder annealed in air at 950℃ is treated as powder (b)
The same etching treatment as above. After drying the powder after each treatment, powder (a), (b),
(c), (d), (e), (f), and (g) were obtained. As comparative examples, powder (h) before etching treatment, that is, after heat annealing treatment, and powder (i) which had just been subjected to a pulverization step were also used. The cumulative particle size distribution of each of these powders (excluding powders (c), (f), and (g)) is shown in Figure 1. Measurement is 0.05
% sodium pyrophosphate aqueous solution. At the same time, the average particle diameter was measured using a specific surface area meter, and the results are shown in Table 3 below. What is noteworthy in Figure 1 is that when the crushed powder is annealed, the particle size becomes coarser, and then various etching treatments can bring the particles closer to the original size, or even light pulverization can make them finer than the original size. It is a point. As will be described later, this was discovered through observation of enlarged photographs, and is because the fine powders aggregate due to heat annealing to form secondary particles. Even if it is possible to organize the irregular phase by annealing, in this aggregated state, uniform dispersion is not possible when mixed with polymers, making it difficult to obtain a dense and high-performance composite piezoelectric material. is expected. If these are pulverized, they will return to individual particles to some extent, but the piezoelectricity will be impaired due to the strain caused by the pulverization. Therefore, chemical etching is effective in separating the particles into individual particles without damaging the piezoelectric properties. As an example, scanning electron micrographs (magnification: 5000x) of powders (d) and (e) are shown in Figures 2a and b, respectively.
As shown in Figure 2, it was found that secondary particles of fused ferroelectric porcelain powder particles were more appropriately dissociated into single crystal particles by etching treatment combined with stirring and mild mechanical disintegration. It will be done. Furthermore, the etching action not only dissociates secondary particles but also dissolves the surface of each particle, so the particle size gradually decreases. It can also be seen that the average particle diameter becomes smaller as the etching treatment time becomes longer and as the mechanical external force becomes stronger. In particular, in the powder (e) obtained by etching treatment combined with rotary mill grinding, there are no particles larger than 7 μm, and the particles are dissociated into single fine particles or small secondary particles smaller than 7 μm. This is the second
This becomes clear if you compare and observe Figures a and b. Figure 1 shows powder (i) and etched powder (a).
As shown in the particle size distribution of ~(e), both etching treatments also have the effect of dissolving ultrafine particles of sub-μm or less (contained approximately 10% in crushed powder (i)). For this reason, one of the effects of etching treatment that cannot be overlooked is that it improves plasticity and fluidity when used as a composite material, leading to increased workability. Figure 3 is a scanning electron micrograph (magnification: 5,000x) of Nb-added lead zirconate titanate porcelain powder that has undergone the usual synthesis-pulverization process (16 hours); Most of the as-applied powder is fragments resulting from mechanical crushing, so the fractured surfaces of the particles are generally sharp, like the edge of a knife. Therefore, if a composite material is made with a flexible polymeric material and an external force is applied to the composite material and the material is changed, the sharp tip may partially cut or puncture the polymeric material, causing mechanical damage. This easily occurs and causes the disadvantage that the composite material is hard and brittle and has low mechanical strength. On the other hand, in the etching process that uses light mechanical pulverization as described above, the etching solution is applied to the inside of the grain boundaries through the cracks generated by applying a light mechanical force to the vitrified grain boundaries that fuse single particles. Because it is a powdering mechanism that penetrates up to the point where the glass phase is easily soluble in acids and dissociates and decomposes it into single particles, it contains almost no broken pieces. It has the great advantage of being able to obtain particles with roundness because it has the function of preferentially dissolving certain parts of the body. As a result, the drawbacks of conventional piezoelectric porcelain powders have been greatly improved, and the powder has a rounded appearance, which improves mechanical strength.It also blends well with polymers, increasing the packing density of the powder. Vacuoles are eliminated, making it possible to mix dense porcelain powder with a high content, thereby increasing the piezoelectric performance of the composite material. Next, the internal differences between these powders were investigated by X-ray diffraction, as shown in Figures 4a and 4b. Chemically etched powder according to the present invention shown in Figure a (b)
For example, compared to the control pulverized powder (i) shown in Figure b, the half-value width of the Kβ line of (200) exhibits a narrower peak, indicating that the crystal lattice is well-aligned and less disordered. This shows that it is a microcrystal close to a single crystal in a single domain with aligned crystal axes. The half width of each powder was 0.170 degrees for powder (b) and 0.315 degrees for powder (i). Next, using these powders (b) and (i), polyvinylidene fluoride (PVDF), which is a polymeric material, was added.
We will discuss the differences in electric field orientation in the domains of sheet-like composite materials mixed at a volume ratio of 3:2 and the differences in their piezoelectric properties. Note that the method for manufacturing the composite material will be described later. These test sheets were _made into _powders (b ) using (Table 3
For sample No. 2), first measure the X-ray diffraction intensity of the (200) and (002) planes on one side, then thinly deposited silver electrodes on both sides, and heat at 150KV/cm in silicone oil at 100℃. Figure 5a shows the results of measuring the X-ray diffraction intensity of the (200) and (002) planes again after polarization was carried out under the conditions of , 30 minutes, and the results using the control pulverized powder (i). Similar measurements were performed on Sample No. 9 in Table 3, and the results are shown in FIG. 5b. Based on these measured values, the X-ray diffraction intensity ratio I (200/I
(002)+I(200) was calculated, and then the domain increment aligned in the electric field direction due to polarization was determined and shown in Table 2. In addition, (200) Kβ of both powders (b) and (i)
The half-value width of is also shown.

[Table] Generally, before polarization, the C-axis direction is
and Z should be oriented with the same probability in the direction of each coordinate axis, and therefore the probability of oriented in the thickness direction of the sheet should be 1/3≒0.33, but for the test sheet using either of the two powders, The reason why it is lower than that is thought to be because the powder particles were oriented in the direction parallel to the rolling surface during calendering during rolling, but in any case, the powder using heat-annealed powder is lower before and after polarization. The X-ray diffraction intensity ratio starts from 0.25.
0.71, the polarization causes a significant orientation of the domains in the direction of the electric field at an increment of 0.46, whereas with the control milled powder virtually no improvement in orientation occurs. In other words, when ferroelectric porcelain powder whose structure has been destroyed by crushing and has become multi-domain or irregular, when mixed with a polymer material, the dot-domain orientation, that is, polarization, is impaired, and this results in the achievement of the expected piezoelectric performance. This is the reason why it is not done. Next, the composite material of the present invention is prepared by mixing each of the previously applied porcelain powders and a polymer such as polyvinylidene fluoride (PVDF) at a volume ratio of 3:2, and adding acetone as a solvent. After the solvent has evaporated, the mixture is heated to 170-180℃ and kneaded with oven rolls, then rolled into a film with a thickness of 0.015-0.05mm and a sheet with a thickness of 0.5mm, with a width of 100mm.
The sample sheet was cut into squares with a length of 150 mm. As shown in the particle size distribution in Figure 1, the powder (h) without etching treatment had 35% remaining particles with a particle size of 15 μm or more, and was rolled into a film with a thickness of 0.025 mm. Since holes are formed everywhere due to the coarse particles or the separation of the particles, short circuits occur between the electrodes due to vapor deposition on the upper and lower surfaces, making it impossible to polarize and impart piezoelectricity. To use (h), double the thickness to 0.050
It was necessary to make it more than mm. However, if the thickness is 0.050 mm or more, the film becomes hard and heavy and cannot be applied to, for example, electroacoustic conversion films for headphone and speakers, or high-sensitivity pyroelectric films with quick response. On the other hand, etching treatment or etching treatment performed while adding mechanical crushing separates the fused coarse particles into single particles and preferentially melts the sharp parts of the particles to make the particles rounded. Even when formed into a thin film of ~0.025 mm, there are almost no holes, and we were able to produce a high-performance piezoelectric film that can withstand practical use. Among these, powder (e) in particular had no coarse particles of 7 μm or more, so it could be molded into a film without forming holes even if the thickness was made as thin as 0.015 mm. A micrograph of this film (225x magnification) is shown in Figure 6a, and it can be seen that a good surface with no pinholes was obtained. On the other hand, in the film molded using the powder (h) without etching treatment, many pinholes due to coarse particles are observed, as shown in Figure b.
In this way, the film using powder (e) was close to the thinness of the film made only of resin, and the piezoelectric polymer composite film was obtained which had piezoelectricity (d constant) twice as large as that of the film made only of resin. Next, thin silver vapor-deposited electrodes were formed on both sides of each film, and the film was placed in silicone oil at 100°C.
Polarization was performed at 150 KV/cm for 30 minutes. For comparison, an FVDF uniaxially stretched film containing no porcelain powder was produced and polarized under the same conditions as above. Proceed to each test sheet above with a width of 20 mm and a length of 70 mm.
The capacitance was measured using a 1V, 1KHz universal bridge, and the relative dielectric constant ε/ε ₀ (where ε
₀ = 8.854×10 ^-12 F/m). In addition, a 45g weight was attached to each specimen, and a 40Hz
A sine wave of 100V/mm is applied, and the elongation that occurs at this time is measured using a differential transformer to determine the piezoelectric strain constant.
Find d ₃₁ = t/V x Δl/l (m/V), and from this calculate the piezoelectric output constant g ₃₁ = d ₃₁ /ε ₀・ε(V・m/N)
The results shown in Table 3 were obtained. In the above formula for calculating the piezoelectric constant, t is the thickness of the piezoelectric sheet (m), V is the applied voltage (V), l is the length of the piezoelectric sheet (m), and Δl is the elongation in the length direction due to voltage application (m). ).

[Table] As a result, in terms of the d constant of piezoelectricity, if the etching conditions such as etching time and external force conditions are appropriately selected, piezoelectricity can be improved as when using powder (b) in Example. It can be greatly improved. Furthermore, if the static etching time is increased, not only will accumulated layers such as impurities, lattice defects, and irregularly shaped layers (glass phase) be removed, but also the particles will become sharper as the particle surface melts and the particles become smaller little by little. Since the vines disappear and the powder becomes more rounded, it becomes a powder that is more suitable for compounding with polymers. For example, when comparing powder (a) that has been stirred for 8 hours only and powder (d) that has been subjected to 88 hours of supervised etching treatment, it is clear from Figure 1 that each particle is gradually smaller. The average particle size is 1.8μm→
1.7 μm, and the piezoelectric constant d value of the composite material is slightly improved compared to the one without standing time, so using porcelain powder that has been properly etched can improve the performance of the composite material. improves. However, as an etching solution for porcelain powder,
In order to use a solution that does not adversely affect the performance of the polymer substance and the composite material, it may sometimes be difficult to dissociate and separate the aggregated and fused secondary particles simply by immersing them in the etching solution. However, in such a case, if an external mechanical force is applied as an auxiliary force, they can be easily dissociated. For example, powder (e) was ground in a rotary mill for 3 hours while immersed in an etching solution. Although some fused secondary particles still remained, there were no particles larger than 7 μm, and most of them were not. The particles are dissociated into single particles, and an excellent powder with a uniform particle size as shown in FIG. 1 is obtained. However, if mechanical pulverization is used in combination with etching, multi-regionalization and irregularity of the crystals will be avoided, resulting in deterioration of piezoelectric performance depending on the degree of pulverization.
When using mechanical grinding in combination, it is important to select appropriate grinding conditions and keep the grinding conditions mild. The powder thus obtained can be processed by conventional grinding,
Since there are no sharp edges or sharp edges found in pulverized powder, the mixture with the polymer becomes more dense and a composite material with fewer vacuoles is obtained, making it a high-performance piezoelectric material. At the same time, the mechanical strength has also been greatly improved, and it has become possible to modify the material into a material that can withstand practical use as a mechanical and electrical transducer without mechanical damage even under repeated impact stress as described below. Next, the piezoelectric polymer composite sheet according to the above example
Durability tests were conducted on No. 2 and the conventional piezoelectric sheet No. 9 against the repeated loads shown in FIG. 7, and the results are shown in the graph of FIG. Experimental method As shown in Fig. 7, samples 2 of 1 cm square and 0.5 mm thick are used for the piezoelectric sheet No. 2 and the conventional piezoelectric sheet No. 9, and these are attached to a base 3 and a buffer steel plate 4 (PVC sandwiched between the plate (thickness 1 mm),
A steel ball 1 weighing 11.8 g was repeatedly dropped from a height of 10 cm, and the output voltage of the sample was measured using a synchroscope 5. The average value of each 10 samples is shown in the graph of FIG. As shown in the graph of Figure 8, conventional product No. 9 broke after an average of 700,000 cycles, but the piezoelectric sheet of the present invention
All No. 2 products operated normally even after 3 million repeated loadings, and no deterioration in output voltage was observed. As described above, according to the present invention, it is possible to realize a piezoelectric polymer composite material that has both the high piezoelectric properties of ferroelectric ceramics and the flexibility of polymer materials.

[Brief explanation of the drawing]

Figure 1 is a particle size distribution comparison diagram of the ferroelectric porcelain powder made of single-domain microcrystals according to the present invention, the porcelain powder when etching treatment is omitted, and the normally pulverized powder. Fig. 3 shows scanning electron micrographs of ferroelectric porcelain powders (d) and (e) obtained by the present invention, and lead zirconate titanate porcelain powder obtained by a conventional synthesis-pulverization method ( Figures 4a and b are the X-ray diffraction diagrams of the porcelain powder according to the present invention (b) and the conventional control powder (i), and Figures 5a and b are the X-ray diffraction diagrams of both these powders (b). , (i) X-ray diffraction diagram showing the change in the X-ray diffraction intensity of the C-axis plane before and after polarization when composited with each polymeric material. Micrograph diagram comparing the surface properties of each composite material using powder and untreated porcelain powder (magnification
225 times), FIG. 7 is a diagram showing a durability test method for a piezoelectric rubber sheet according to the present invention, and FIG. 8 is a graph showing the results of a durability test for a piezoelectric rubber sheet. 1... steel ball, 2... piezoelectric sheet, 3... base,
4...Buffer steel plate, 5...Synchroscope.

Claims (1)

[Claims] 1. Synthesis by solid-phase reaction through mixing of blended raw material powders according to a predetermined chemical composition, pulverization, heat annealing treatment, and chemical etching treatment to produce particles with substantially uniform particle size. A piezoelectric polymer composite material comprising a mixture of ferroelectric porcelain powder consisting of single-domain microcrystals and a polymer substance. 2 Synthesis by solid-phase reaction through mixing raw material powders according to a predetermined chemical composition, and particle size reduction through pulverization and heat annealing treatment, mechanical crushing, or chemical etching treatment including light pulverization. 1. A piezoelectric polymer composite material comprising a mixture of a ferroelectric porcelain powder consisting of substantially single-domain microcrystals and a polymeric substance.