JP2676385B2 - Piezoelectric composite material for hydrophone - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention is one in which piezoelectric ceramic powder is blended with synthetic rubber or the like, and sends sound waves or ultrasonic waves into water, or conversely propagates in water. The present invention relates to a piezoelectric composite material for a hydrophone that can be applied as a hydrophone that receives sound waves or ultrasonic waves.

<Prior Art> A piezoelectric composite material obtained by mixing piezoelectric ceramic powder such as lead titanate in a synthetic rubber has a lower sound velocity of a sound wave propagating in a medium at a lower density than that of a general sinter piezoelectric ceramic. It is suitable as a piezoelectric composite material for a hydrophone such as a hydrophone because it has good acoustic matching with water and its flexibility makes it less susceptible to water pressure even when immersed deep in water.

<Problems to be Solved by the Invention> Piezoelectric composite materials for hydrophones are required to have as high a wave receiving sensitivity in water as possible. However, a material having a high wave receiving sensitivity is a hydrostatic pressure of the wave receiving sensitivity. It turned out that it is likely to be dependent.

An object of the present invention is to resist a piezoelectric composite material for a hydrophone of this type, which has high wave receiving sensitivity and low hydrostatic pressure dependency.

<Means for Solving Problems> The present invention relates to a piezoelectric composite material for a hydrophone, which is obtained by mixing piezoelectric ceramic powder with a vulcanizing agent in a synthetic rubber, molding the mixture, and further polarizing the piezoelectric ceramic powder. Is composed of two or more kinds of powder materials having different average particle diameters, and the compounding ratio of piezoelectric ceramic powder / synthetic rubber is
It is characterized by being 65 to 75 (volume%).

<Operation> It is considered that the hydrostatic pressure dependency is due to the presence of an air layer between the porcelain powders in the piezoelectric composite material. However, two or more kinds of powder materials having different average particle diameters are used as piezoelectric ceramic powder /
When the synthetic rubber compounding ratio is mixed in the range of 65 to 75 (volume%), compared to a single powder material with the same average particle size, particles with different particle sizes are mixed intricately and filling efficiency is improved. Is improved, which reduces the air layer between the particles. Therefore, the hydrostatic pressure dependency is reduced.

The deviation between the measured density and the theoretical density of the piezoelectric rubber sheet drastically decreases when the piezoelectric ceramic powder / synthetic rubber compounding ratio exceeds 75%. In this region, it is estimated that an air layer is contained in the piezoelectric rubber sheet, and therefore, this compounding ratio becomes the upper limit. Further, if the piezoelectric ceramic powder / synthetic rubber compounding ratio is less than 65%, sufficient wave receiving sensitivity cannot be obtained. Therefore, this mixing ratio becomes the lower limit.

<Example> Commercially available PbO with a purity of 99% or more (average particle size of 3 μm or less) and TiO ₂ with a purity of 99.5% or more were compounded under the composition formula of PbTiO ₃ , 2.5 Kg was weighed, and alumina boulder was added with a vibration mill. Dry mixing was carried out at (3.5 Kg) for 3 hours. At this time, the inner wall of the pot of the vibrating mill was lined with urethane resin to prevent impurities from being mixed.

Next, a tablet with an outer diameter of 47 mm, a thickness of 5 mm, and a press density of 4.5 g / cm ³ is made by pressurizing at 350 Kg / cm ² using a mold, and a solid phase reaction is performed in a high alumina crucible at 1050 ° C. for 2 hours. It was Thereafter, the high-temperature mass was put into a cooling water tank to cause rapid cooling in water to obtain fine particles. Furthermore, in order to promote disintegration, stirring was carried out for 5 hours or more using a propeller stirrer. The lead titanate powder thus formed was drained of water, dried at 100 ° C. for 24 hours, and then passed through a sieve to separate two types (32 μm, 7 μm) of porcelain powder having an average particle size group.

Next, the ratio of 32 μm / 7 μm is 0
In the range of up to 100 (wt%), every 25% was prepared and mixed, and a plurality of mixed powder samples were manufactured.

Then, each of the mixed powders was mixed with a synthetic rubber made of neoprene rubber as a synthetic rubber in various compounding ratios.
The lead titanate mixed powder (piezoelectric ceramic powder) / synthetic rubber was compounded at a compounding ratio of 50 to 80% by volume, and every 5%. Furthermore, as a vulcanizing agent, Pb ₃ O ₄ , ZnO and dibenzothiazyl disulfide (trade name; Nocceller DM)
Was mixed. The compounding ratio of the vulcanizing agent was Pb ₃ O ₄ : ZnO: Noccer DM = 20 parts by weight: 5 parts by weight: 0.5 parts by weight with respect to 100 parts by weight of the synthetic rubber.

Furthermore, this is roll-molded with a small roll machine, and the temperature is 170
Under the conditions of ℃, pressure 140Kg / cm ² and time 15 minutes, it is cross-linked by vulcanizing press and molded into a sheet with a thickness of 1mmt. Formed.

Then, this sheet was immersed in an insulating solution at 20 ° C., and a DC voltage of 70 KV / cm was continuously applied in the solution for 1 hour,
Polarization treatment was performed to obtain a piezoelectric rubber sheet for a hydrophone (piezoelectric composite material).

Then, the change in the wave receiving sensitivity of each piezoelectric rubber sheet under a predetermined hydrostatic pressure was measured. For this measurement, a wave receiving sensitivity measurement water tank using a Florinate solution was used. The hydrostatic pressure dependence was measured as the decrease value of the receiving sensitivity when changing from 5 Kg / cm ² to 150 Kg / cm ² .

On the other hand, the deviation between the theoretical density and the measured density was measured for each material. The density was determined by measuring the gravity in the air and the weight in the flow linen liquid on the piezoelectric rubber sheet, and compared with the density of each raw material and the theoretical density obtained by the compounding ratio.

Further, the M _L value, which is a target for ease of molding during vulcanization molding of the piezoelectric rubber, was measured using a curast meter.

<Experimental Results> FIG. 1 shows the wave receiving sensitivity of the piezoelectric rubber sheet at each compounding ratio. FIG. 2 shows the hydrostatic pressure dependence of the wave receiving sensitivity of the piezoelectric rubber sheet at each compounding ratio.

With these, the compounding ratio of piezoelectric ceramic powder / synthetic rubber is 60%.
Up to -205 to -206 dB, the sensitivity to hydrostatic pressure is as low as 1 dB or less. Increasing the blending ratio also increases the sensitivity to waves, but the hydrostatic pressure is almost proportional to this. It can be seen that the dependence increases.

For example, when the piezoelectric ceramic powder / synthetic rubber compounding ratio = 65% and the powder particle size compounding ratio = 100%, which gives the highest wave sensitivity,
It shows the highest sensitivity of -198.4 dB, but also has a hydrostatic pressure dependency of 5.3 dB.
And is the best. On the other hand, the piezoelectric ceramic powder / synthetic rubber compounding ratio showing the second highest wave sensitivity = 70%, powder particle size compounding ratio = 0
% Is -201.1 dB, but the hydrostatic pressure dependence is
It is relatively small at 2.7 dB.

From Fig. 1, it can be seen that the compounding ratio of piezoelectric ceramic powder / synthetic rubber is 65
It is understood that if it is less than%, sufficient wave receiving sensitivity cannot be obtained.

Next, FIG. 3 shows the change in ε ₃₃ ^T / ε ₀ with respect to the piezoelectric ceramic powder / synthetic rubber compounding ratio, the deviation between the measured density and the theoretical density of the piezoelectric rubber sheet, and the hydrostatic pressure dependence of the wave sensitivity. .

The difference between the measured density of the piezoelectric rubber sheet and the theoretical density is
When the compounding ratio of piezoelectric ceramic powder / synthetic rubber is 60%, it is about + 3%, which is almost constant, but when it exceeds this value, it gradually decreases,
In particular, when the powder particle size compounding ratio = 0%, it sharply decreases in the region where the piezoelectric ceramic powder / synthetic rubber compounding ratio = 75%. In this region, it is estimated that the piezoelectric rubber sheet contains an air layer.

Here, ε ₃₃ ^T / ε ₀ increases almost linearly as the compounding ratio of piezoelectric ceramic powder / synthetic rubber increases, but
In the area exceeding%, this straight line is lowered, showing a good agreement with the deviation between the measured density and the theoretical density.

As an aside, PVD containing porous PZT and air layer
In F, hydrostatic pressure dependence appears, and it is reported that the air layer and hydrostatic pressure dependence is related to density.

Regarding the wave sensitivity and the hydrostatic pressure dependency, the causal relationship between the deviation between the measured density and the theoretical density and the change in ε ₃₃ ^T / ε ₀ is not shown in the figure. This suggests that the air layer and hydrostatic pressure dependence are related, but quantitatively, other factors should also be introduced for consideration.

Thus, as shown in FIG. 3, when the piezoelectric ceramic powder / synthetic rubber compounding ratio is 65 to 75 (volume%) and two types of powder particle sizes are compounded, a compound having a single average particle size is It was found that the dependence on static pressure is reduced without impairing the receiving sensitivity.

Fig. 4 shows the deviation between the measured density and the theoretical density of the piezoelectric rubber sheet with respect to the powder particle size mixture ratio, and the curast meter M
Shows hydrostatic pressure dependence of _L value and receiving sensitivity. As a result, each value shows a maximum and a minimum in the vicinity of the powder particle size mixture ratio = 50%. In other words, the powders with 32% and 7 μm mixed in 50% each have a higher density than those with a powder particle size of 32 μm alone and 7 μm alone, and the curability meter M _L value becomes smaller, resulting in better moldability and hydrostatic pressure. It can be seen that the dependency can also be reduced. It is considered that this is because mixing the particle diameters of different piezoelectric ceramic powders enhances the filling effect, so that the amount of the air layer can be reduced.

In the above-mentioned experiment, powder materials having two average particle sizes of 32 μm and 7 μm were mixed, but the mixing efficiency can be increased and the hydrostatic pressure dependency can be reduced by mixing two or more kinds of powder particles. it is conceivable that.

<Effects of the Invention> The piezoelectric composite material of the present invention comprises piezoelectric ceramic powder with two or more kinds of powder materials having different average particle sizes, and the piezoelectric ceramic powder / synthetic rubber compounding ratio is 65 to 75 (volume). %), The required wave receiving sensitivity can be obtained, and the hydrostatic pressure dependency is low. Therefore, even if the hydrostatic pressure changes, a stable high output can be obtained. There is an excellent effect that it can be obtained.

[Brief description of the drawings]

1 is a graph showing the wave receiving sensitivity of the piezoelectric rubber sheet at each mixing ratio, FIG. 2 is a graph showing the hydrostatic pressure dependency of the wave receiving sensitivity of the piezoelectric rubber sheet at each mixing ratio, and FIG. 3 is the piezoelectric Graphs showing changes in ε ₃₃ ^T / ε ₀ with respect to porcelain powder / synthetic rubber compounding ratio, deviation between measured density and theoretical density of piezoelectric rubber sheet, and hydrostatic pressure dependence of wave sensitivity, respectively. 6 is a graph showing the difference between the actually measured density and the theoretical density of the piezoelectric rubber sheet with respect to the diameter mixture ratio, the curastometer _ML value, and the hydrostatic pressure dependence of the wave receiving sensitivity.

Claims (1)

(57) [Claims] 1. A piezoelectric composite material for a hydrophone obtained by mixing piezoelectric ceramic powder with a vulcanizing agent in a synthetic rubber, molding the mixture, and polarizing the composite, wherein the piezoelectric ceramic powder has different average particle diameters. Composed of two or more types of powder materials, with a piezoelectric ceramic powder / synthetic rubber mixing ratio of 65
Piezoelectric composite material for hydrophone, characterized by being ~ 75 (volume%).