JPS6131639B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a highly fractionated composite piezoelectric material. Generally, attempts to obtain this type of piezoelectric material by combining ferroelectric ceramic powder with a polymer substance are known, but conventionally, ferroelectric materials such as BaTiO ₃ , PbTiO ₃ or PbZrO ₃ −PbTiO ₃ solid solution have been used. After producing porcelain by solid phase reaction under heating or synthesizing single crystals such as potassium sodium niobate (PSN), they are usually crushed using a crusher such as a ball mill or a vibration mill to obtain the desired particles. Since it was used in the form of simply crushed powder adjusted to a certain size,
The piezoelectric properties were significantly different from those expected from the ferroelectric ceramic itself as described above, and only low performance was obtained. 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 found that in the crushing process performed after solid phase reaction or single crystal synthesis, It is unavoidable that structural destruction occurs in the microcrystal, resulting in the generation of countless domains or irregular phases, and these multi-regional divisions or irregular phases within the microcrystals lead to the formation of complexes with polymeric substances. Regarding the effective electric field that acts on the porcelain powder when polarization treatment is performed after the oxidation process,
Coupled with the fact that the dielectric constant of the polymer material is significantly reduced from several tens to several hundredths, this significantly impedes orientation, and therefore even at high voltages close to the withstand voltage of composite materials. Even if it is polarized, most of the domains are no longer aligned in the direction of the electric field when the electric field is reduced as described above, and therefore sufficient piezoelectricity cannot be achieved.In the end, porcelain powder or single crystal is mixed with the polymer material. I realized that the technical significance of this was almost negligible. As a result of numerous experiments and studies, the inventors discovered the following: by applying heat annealing to the porcelain powder that had undergone the crushing process as described above, it was possible to obtain a single fraction after synthesis before crushing. Ferroelectric porcelain powder that has returned to microcrystals close to a single domain can be obtained, and ferroelectric porcelain powder consisting of microcrystals close to a single domain, on the other hand, can be composited with a specific amount of a polymeric substance. As a result, outstanding performance that has never been matched as a piezoelectric polymer composite material can be realized in the manufacturing process.
It has been discovered that this method can be realized without any difficulties in the process. We mix raw material powders that correspond to the ferroelectric porcelain composition that we are trying to make, and after mixing, heat synthesis.
After that, it is assumed that the powder is crushed to a desired particle size, and this crushed powder is subjected to a subsequent annealing treatment to obtain a microcrystalline powder having a nearly single domain. 1 Heat the crushed powder in its powder form. The heating temperature is preferably in the range of 600 to 1200°C. 2. Heating is performed in the atmosphere or in an atmosphere with a higher oxygen concentration. 3. It is desirable to repeat the heat annealing process 2 to 4 times. The ferroelectric porcelain powder obtained in this way is subjected to a normal powder crushing operation as a means of pulverization, so that it can be adjusted to any desired particle size (from submicrons to several tens of microns). Moreover, since the multi-domain division and irregularity within the microcrystal due to the structural destruction accompanying this fragmentation are restored and removed by heating annealing, it can be considered that the microcrystal consists of a nearly single domain. Of course, strictly speaking from the viewpoint of condensed matter theory, the composite before fracture is not already a perfect single-domain crystal, but contains impurities and structural irregularities (lattice defects, layer defects, etc.). Or, due to deviations from stoichiometry, non-uniform composition, or even external factors (heat, stress), some domain formation can be seen, and this cannot be avoided given the current level of science and technology. It is a self-evident fact that
In addition, even by applying heat annealing as described above, it does not completely return to the domain structure before fracture, but the domain structure in the crystal that remains after heat annealing is small enough to be affected by the voltage at the time of polarization. The inventors have found that the above-mentioned method is not a factor that hinders alignment in the direction of the applied electric field or orientation to the electric field, and exhibits characteristics that indicate de facto directionality. Powders that have almost recovered to the state immediately before crushing by heating annealing are defined as de facto single-domain microcrystalline particles. On the other hand, if the powder is left as it is by crushing after heating synthesis by conventional conventional means, countless multi-region and irregularities occur due to structural destruction of the crystal, and as mentioned at the beginning, alignment in the direction of the electric field occurs. It is almost no longer seen. Therefore, the distinction between these multi-domain crystal grains and single-domain microcrystal particles is clear, but the term "single-domain microcrystal" does not necessarily mean that it is ideal. Heat-annealed ferroelectric porcelain powder consisting essentially of single-domain crystal grains can be mixed with various polymeric substances, formed into any desired shape, such as a sheet, and subjected to a hardening process such as cross-linking or vulcanization. Polarization can be effected advantageously through . Here, even if the effective electric field becomes extremely low, ranging from tens to hundreds of times lower than the dielectric constant of the polymer material, the stress caused by powdering causes structural destruction in countless domains within the microcrystals. It has been confirmed that because it is not accompanied by ferroelectric and piezoelectric properties, it is easily aligned in the direction of the electric field and exhibits particularly high ferroelectric and piezoelectric properties. Ferroelectric ceramic powder consisting of single-domain microcrystalline particles has unidirectionality with excellent orientation in the polarization direction by compounding with polymers at various blending ratios, and when compounded, Particularly good workability. Therefore, for example, transducers for living bodies that require flexibility that is compatible with the human body are made with a high polymer content, and keyboard switches that have a large number of switches integrated on a piezoelectric sheet are used.
For items that require higher piezoelectric performance even if they are somewhat less flexible, a high proportion of ferroelectric porcelain powder is used. Depending on the selection, it is possible to provide composite piezoelectric materials with mechanical, electrical, and physical properties that suit a wide range of applications, and they can be used not only for mechanoelectric conversion and electroacoustic exchange, but also as pyroelectric materials in the future. This means that it can be expected to be applied to a wide range of fields. In this specification, piezoelectricity means electrostrictive action in a broad sense, including all of the above-mentioned transformations. However, in known piezoelectric sheets using porcelain powder that could not avoid multi-regionalization due to conventional crushing, the polarization was severely inhibited as described above. As a result, the mixed sheet with the polymer material became hard, brittle, and easily torn at each stage of productization, and could not be put to practical use.
However, in the present invention, it is not necessary to use such a high proportion, so the flexibility of the polymer material itself is advantageously maintained, and a sufficiently high piezoelectric performance is achieved regardless of this. For the first time, a practical application for a piezoelectric polymer composite material that combines both characteristics has been established. Regarding the blending ratio (volume ratio) of the piezoelectric ceramic powder and the polymeric substance, if it is less than 1:9, no effective field is recognized for blending these ceramic powders, and as the blending amount increases with this as the lower limit. Therefore, the piezoelectricity improves, especially from around 55:45, but
If the ratio exceeds 9:1, the fluidity and processability of the mixture will deteriorate significantly, making molding virtually impossible and therefore impractical, so a blending ratio of 1:9 to 9:1 is desirable. . The present invention can be suitably carried out in single-component systems, multi-component systems of ferroelectric ceramics having the following various crystal structures, as well as those obtained by substituting or adding/transforming the same as the basic composition. I can do it. 1 Perovskite structure (1) Barium titanate and a solid solution centered on it BaTiO ₃ , (Ba, Pb, Ca)TiO ³ ..., etc. (2) Lead titanate and a solid solution centered on it,
_PbTiO3 , (Pb, La) _TiO3 , _PbTiO3−
BiFeO ₃ , etc. (3) Lead zirconate titanate and solid solutions centered on it, 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⁺ (B _1/3 ^{2 +} , B _2/3 ⁵⁺ ) O ₃ For example, Pb (Ni _1/3 , Nb _2/3 ) O ₃ , Pb
(Zn _1/2 , Nb _2/3 ) O ₃ , Pb (Co _1/3 ,
Nb _1/3 ) O ₃ , Pb (Mg _1/3 , Nb _2/3 ) O ₃ ,
... ^{etc .} b _{For example} ^, _{Pb(Ni 1/2 ,} W _{1/
2 )} O ₃ ^, Pb (Co _{1/2 ,} W _{1/2 )} ^O ₃ ..., etc. c For example, ^Pb ( Fe _1/2 ,
Nb _1/2 ) O ₃ , Pb (Sb _1/2 , Nb _1/2 ) O ₃ ,
Pb(Y _1/2 , Nb _1/2 ) O ₃ ..., etc. (5) Sodium niobate and solid solutions centered on it, such as NaNbO ₃ , (Na, K)NbO ₃ , Na
(Ta, Nb) O ₃ ... etc. 2 Tungsten bronze structure PbNb ₂ O ₆ , PbNb ₂ O ₆ −PbTa ₂ O ₆ , PbNb ₂ O ₆ −
BaNb ₂ O ₆ ... etc.3 Viscose layered structure 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 The basic composition is the above-mentioned component system, and some of the Pb is replaced with an alkaline earth metal. 6 The basic composition is the above-mentioned component system, and one or more selected from the following groups (), (), and () are added as accessory components and modified () Nb ₂ O ₅ , Ta _{2O5 , La2O3 , Sb2O5 ,}
Sb ₂ O ₃ , Bi ₂ O ₃ , WO ₃ etc. () MgO, Fe ₂ O ₃ , SO 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 composite piezoelectric materials with a wide range of properties suitable for various applications. Next, according to the present invention, the polymeric substance capable of decoupling the above-mentioned ferroelectric porcelain, especially the porcelain powder consisting of virtually single-domain microcrystalline particles, can be made of various types of rubber, including natural, artificial, and synthetic. and recycled rubber or blended rubber thereof, especially fluorocarbon rubber and chloroblend, and thermoplastic resins such as polyvinylidene fluoride (PVDF), acrylonitrile-butadiene-styrene copolymer (ABS), vinyl chloride (PVC), Examples include polyvinyl fluoride (PVF). Examples of the present invention will be described below. Example 1 〓〓〓〓〓
Commercially available PbO and _WC3 with purity above 99%, 98.5%
Using _the above ZrO ₂ and 98% or more TiO ₂ , they are blended according to the composition of Pb (Ti _{0.5 -} Zr _0.5 ) O ₃ + 1% by weight WO ₃ to be made, and the total purity of these is 99%. 2.5 kg of the above ingredients were weighed out and mixed in a dry manner for 5 hours using a vibrating mill. At this time, the lining of the vibrating mill was lined with urethane resin, and alumina cobbles were used to prevent contamination with impurities. This mixed powder is packed into a high alumina crucible.
The mixture was maintained at 730° C. for 4 hours in a PbO atmosphere, and Pb(Ti _{0.5 −Zr 0.5} )O ₃ + ₁ % by weight WO ₃ was synthesized by solid phase reaction. From this, 200 g of synthetic powder was separated, and 300 g of alumina cobbles and acetone were charged into it using a 2-volume alumina ball mill, and pulverized for 16 hours. After drying, coarse particles are removed using a 60-mesh mesh and divided into two parts, one of which is used as a control pulverized powder, and the other is placed in a smaller rotary kiln in an atmosphere with an oxygen concentration higher than or equal to the atmosphere at the maximum temperature inside the furnace. 800
A heat annealing treatment was performed at ˜950°C to obtain a heat annealed powder. The annealing process is approximately
It was set as 15 minutes. The differences between these powders were investigated by X-ray diffraction, as shown in Figures 1a and 1b. The heat-annealed powder a according to the present invention exhibits a narrower peak in the half-width of the Kβ line of (200) than the control crushed powder b, indicating that the crystal lattice is well-aligned and less disordered. This shows that it is a microcrystal close to a single crystal with a single domain with aligned crystal axes. The half-width of each powder was 0.195° for powder and 0.345° for powder b. Next, these powders a and b are mixed with polyvinylidene fluoride (PVDF), which is a polymeric substance, and 3:
We will discuss the differences in the electric field orientation of the domains and the piezoelectric properties of the composites when mixed at a volume ratio of 2. Both porcelain powders are made of polyvinylidene fluoride (PVDF) with 2% by weight of stearic acid as a mold release agent.
were mixed in a volume ratio of 3:2, acetone was added as a solvent, and after the solvent had evaporated, the mixture was heated to 170-180°C, kneaded with open rolls, and rolled into a sheet with a thickness of 0.05 mm. A test sheet was prepared by cutting it into squares with a width of 100 mm and a length of 150 mm. These test sheets were made using annealed powder that was heat-annealed twice for 2 hours at 950°C in an O ₂ atmosphere (O ₂ concentration 38%) (Table 2 No. 6). After measuring the X-ray diffraction intensity of the (200) and (002) planes, thinly deposited silver electrodes were formed on both sides, and polarization was performed in silicone oil at 100°C at 150 KV/cm for 30 minutes. The X-ray diffraction intensities of the (200) and (002) planes were measured again, and the results are shown in Figure 2a, and the results of a similar measurement using a control crushed powder are shown in Figure 2b. Based on these measured values, the X-ray diffraction intensity ratio of the C-axis plane before and after polarization (002)/
(002)+(200) was calculated, and then the domain increment aligned in the direction of electrolysis due to polarization was determined and shown in Table 1. The half-value widths of (200)Kβ of both powders a and b are also shown.

[Table] Generally, before polarization, the C-axis direction is
and Z should be oriented with the same probability in each coordinate axis direction, and therefore the probability of oriented in the thickness direction of the sheet should originally 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 that it is parallel to the rolling surface during calender forming during rolling.
This is thought to be due to the powder particles being oriented in the same direction, but in any case, the X-ray diffraction intensity ratio before and after polarization was 0.26 for those using heat-annealed powder.
0.69, the polarization causes a significant orientation of the domain in the direction of the electric field at an increment of 0.43, whereas with the control 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 test sheet obtained as described above,
Cut into pieces 20mm wide and 70mm long, measure the capacitance with a 1V, 1KHz universal bridge, and calculate the dielectric constant ε/
Calculate ε ₀ (here ε ₀ = 8.854×10 ^-12 F/m), attach a 45 g weight to each specimen, apply a 40 Hz sine wave at 100 V/mm, and calculate the elongation that occurs at this time. Measured with a differential transformer, piezoelectric strain constant d ₃₁
= t/V×Δl/l (m/V), and from this a performance test was performed to determine the piezoelectric output constant g ₃₁ = d ₃₁ /ε ₀・ε(Vm/N).
Table 2 shows the performance of various annealed powders in different atmospheres and times in comparison with the control crushed powder.
It was shown to.

[Table] As shown in Table 2, the annealing temperature is
Before 950℃, especially when the concentration of oxygen atmosphere is high and when the number of annealing is 2 to 4 times, the annealing effect becomes the largest and excellent characteristics can be obtained, but when the number of annealing reaches 8 times, defects due to evaporation of PbO occur. and fusion phenomenon between particles occurs,
Performance is getting worse. In any case, by the heat annealing treatment according to the present invention, the piezoelectric constant d ₃₁ is 3 to 5 times that of the control pulverized powder, the g ₃₁ is 2.3 to 3.3 times, and the dielectric constant is
An improvement of 1.2 to 1.5 times can be seen. The polymer composite piezoelectric material of the present invention can obtain high piezoelectric performance without losing the characteristics of a polymer material, and can be used as an electro-mechanical conversion material, an electroacoustic conversion material, or a pyroelectric material to convert pressure, light, or heat into electricity. On the other hand, as sheets or films that convert electricity into displacement or vibration, high piezoelectricity can be used in fields that utilize the flexibility of polymeric materials, such as acoustic transducers, physical measurements, and in particular, blood pressure monitors, pulse monitors, heart rate monitors, and heartbeat microphones. It has a wide range of applications, including areas such as piezoelectric keyboard switches, etc. As described above, according to the present invention, it is possible to create a polymer composite piezoelectric material that combines the high piezoelectric properties of ferroelectric porcelain and the flexibility of polymer materials without significantly impeding the characteristics of both. It can be realized. 〓〓〓〓〓

[Brief explanation of the drawing]

Figures 1a and b are X-ray diffraction diagrams of the magnetic powder according to the present invention and a conventional control crushed powder, and Figures 2a and b are
It is an X-ray diffraction diagram showing the change in the X-ray diffraction intensity of the C-axis plane before and after polarization when both of these powders are combined with a polymeric material. 〓〓〓〓〓

Claims (1)

[Claims] 1. A ferroelectric material consisting of practically single-domain microcrystalline particles by synthesis into a porcelain composition exhibiting ferroelectricity, crushing, and annealing in the atmosphere or in a high-temperature atmosphere with an oxygen concentration higher than that of the ferroelectric material. A polymer composite piezoelectric material comprising a mixture of porcelain powder and a polymer substance. 2 The mixing ratio of porcelain powder and polymeric substance is 1:9 ~
9:1 piezoelectric material according to claim 1.