JPS5821315A - Method of producing composite pyroelectric element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a composite pyroelectric material, and in particular, after manufacturing a polycrystalline pyroelectric material by layering pyroelectric crystal particles with polar orientation, The present invention relates to a method of manufacturing a composite pyroelectric material by impregnating it with a binder.

First, the pyroelectric material in the present invention will be explained.

In general, piezoelectric materials exhibit electrical spontaneous polarization (5 pontane polarization).
-ous polarization) Ps can be classified into pyroelectric materials and pyroelectric materials depending on the presence or absence of Ps, and pyroelectric materials can be classified into pyroelectric materials depending on whether the spontaneous polarization Ps can be reversed in direction by an electric field or not. It can be classified into ferroelectric materials and non-ferroelectric materials. All pyroelectric materials can also be used as piezoelectric materials, and some pyroelectric materials can also be used as ferroelectric materials. The unique properties of the pyroelectric substance itself are:
Pyro-electric effect
), that is, it is known that when a part of a material is heated, an electric charge appears on its surface, and this property is being utilized to be applied to, for example, infrared sensors, heat-sensitive elements, etc.

Here, the pyroelectric substance usually takes the form of a single pyroelectric crystal, a polycrystal, a sieve, or a composite with another substance. In general, in order to obtain a single crystal, equipment costs,
Material costs are high, manufacturing time is long, and it is difficult to produce large-sized or arbitrarily shaped single-crystal pyroelectric materials. On the other hand, polycrystals and composites are advantageous in terms of equipment costs, material costs, and manufacturing time, and they also have the advantage of being easy to manufacture in large sizes and in arbitrary shapes. There is also.

In addition, since the polycrystalline pyroelectric material described above is composed only of pyroelectric crystal material, it can produce a larger pyroelectric effect than the above-mentioned composite pyroelectric material. A conventional method for producing an electric body uses, as a raw material, pyroelectric crystal particles or powder, such as BaTL03, in which the spontaneous polarization P8 of the ferroelectric substance relatively easily reverses direction (switching). After the pyroelectric crystal particles are accumulated or stacked and sintered, so-called poling is performed in which an electric field is applied to align the spontaneous polarization Ps in substantially the same direction. However, the raw materials are limited to ferroelectric pyroelectric crystals that can be inverted relatively easily, and ferroelectric materials that are virtually impossible to invert and non-ferroelectric pyroelectric materials are used. Therefore, it was not possible to produce polycrystalline pyroelectric materials or composite pyroelectric materials. Furthermore, even if poling is performed after the above sintering, it is almost impossible to completely match the directions of the spontaneous polarization Ps, and it is difficult to obtain pyroelectric properties comparable to the above single crystal pyroelectric material. .

Therefore, the present inventor proposed that when pyroelectric crystal particles are laminated on an electrode substrate in which an electric field is formed perpendicularly to the plate surface by electrophoretic electrodeposition method or atomization method, the temperature changes in the crystal particles. A method for producing a pyroelectric material has already been proposed in which a laminated particle layer with oriented pyroelectric axes is obtained by giving The object of the present invention is to produce a composite pyroelectric material having a high packing density of pyroelectric crystal particles by impregnating the pyroelectric material produced by the above method with a bonding agent.

That is, the characteristics of the method for manufacturing a composite pyroelectric material according to the present invention include a step of laminating pyroelectric crystal particles on a substrate with the pyroelectric axis oriented to obtain a polycrystalline pyroelectric layer; The method consists of a step of impregnating the crystalline pyroelectric layer with a binder.

Here, as the binder, thermoplastic or copolymerizable organic materials can be used, such as paraffin, copolymers of vinyl chloride, vinyl acetate, polyurethane, epoxy resins, polyester resins, etc. Solutions may be used singly or in combination. In addition, this binder also includes those that are decomposed or combined by heating etc. to finally become a binder. For example, an aqueous solution of boric anhydride and vinegar or lead is It is also possible to use mixed materials from which lead-based glasses are obtained.

Next, prior to a detailed explanation of the present invention, the general properties of pyroelectric crystal particles will be explained with reference to FIG. 1 ASB.

FIG. 1A schematically represents the internal state of the pyroelectric crystal particle 1 in a steady state. The arrows in the figure indicate the electrical spontaneous polarization Ps, and electric dipole).

Then, one arrow P8 and a pair of internal charges ■ and O are
In the steady state shown in Figure 1A, the spontaneous polarization Ps and the internal charge pairs that cancel or neutralize it exist in equal amounts, so the pyroelectricity The apparent electric charge and the apparent electric dipole from the outside of the sexual crystal particle 1 are zero. For example, if the spontaneous polarization Ps decreases as shown in FIG. 1B by applying a temperature change to the pyroelectric crystal particle 1 in such a steady state, the amount of internal charge pairs will be much larger than Ps. The internal charge pair of this difference effectively appears as 0. In other words, the pyroelectric crystal particle IK appears to have an electric dipole as shown by the arrow Peff in FIG. 1B. After the above-mentioned temperature change, due to the so-called slow rolling phenomenon that accompanies a time change according to the dielectric relaxation time, for example, the charge pairs of the above-mentioned difference combine and disappear, resulting in an equilibrium state in which the amounts of the internal charge pairs and Ps are equal to each other ( steady state).

In addition, depending on the direction of temperature change (temperature increase or temperature decrease),
The change in the amount of spontaneous polarization PsO is also different, and when Ps increases more than the internal charge pair, the apparent electric dipole Pe
Of course, ff appears in the same direction as Pg, and the relaxation phenomenon results in the generation of a new internal charge pair.

Next, there is an electrophoretic electrodeposition method (or simply called an electrodeposition method).

) In general, when solid particles are dispersed in a liquid, the solid particles have a positive or negative charge in the liquid. teeth,
It has a negative charge. Then, when two electrodes 3 and 4 that are separated from each other and face each other are arranged in this dispersion liquid 2, and a DC voltage from a DC power source 5 is applied between both electrodes 3 and 4, the dispersed particles 1 are The particles move (electrophoresis) toward the positive electrode 3 and are deposited and stacked on the surface of the electrode 30 serving as a substrate. This phenomenon is used as an electrophoretic electrodeposition method for painting, etc. In addition, when the dispersed particles have a positive charge, it goes without saying that they electrophores toward the negative electrode.

Here, in the method for manufacturing a pyroelectric material using electrophoresis, which is the premise of the present invention, the above-mentioned dispersed particles include, for example, L
Pyroelectric crystal particles containing LNb03-LLTaOs, naT=Os, zircon-lead titanate-based materials (so-called PZT, etc.), and other ferroelectric and non-ferroelectric materials are used, and the dispersion liquid is, for example, A liquid with high resistivity (TE>10'Ωcrn) such as trichlorethylene is used. Furthermore, all the crystal particles are made to undergo temperature changes almost uniformly, such as increasing or decreasing temperature, until the crystal particles adhere to and are fixed on the electrode surface, which also serves as a substrate, by electrophoresis caused by the electric field. For this purpose, it is sufficient to provide the dispersion with a temperature distribution that extends in the direction of electrophoresis, or to heat or cool the entire or part of the liquid. In addition, the crystal particles facing the electrode surface may be directly heated by electromagnetic radiation such as light or microwaves with wavelengths that are easily absorbed by the particles, and in this case, the crystal particles may be colored in accordance with the absorption wavelength. It is preferable that the crystal particles are previously subjected to a surface treatment such as the following.

In this way, all particles approaching the electrode surface under an electric field will undergo a uniform temperature change, and due to the pyroelectric effect described above, they will have an electric dipole corresponding to pyropolarity. , is deposited on the electrode surface with polar orientation under the above electric field. By taking out this deposited layer from the liquid and drying it, a polar oriented pyroelectric crystal particle layer, that is, a polycrystalline pyroelectric material is obtained.

In addition, in another method for manufacturing a polycrystalline pyroelectric material, which is a premise of the present invention, that is, a method using a fog method, the pyroelectric crystal particles are prepared using a material having a high resistivity (for example, ';
A colloidal liquid is created by dispersing it in an organic liquid of about 10Ωm), and by atomizing this colloidal liquid onto the substrate electrode surface to which an electric field is applied perpendicularly to the surface, polarity is created on the surface of the substrate. A polycrystalline pyroelectric material is obtained by stacking layers of crystal grains with oriented (polarly oriented) pyroelectric axes including the pyroelectric components, and drying the organic components by evaporating or decomposing them.

Since the polycrystalline pyroelectric material thus obtained has relatively weak bonding forces between particles and between particles and the substrate, it is often fired at high temperatures to form a sintered body. In cases where the conductive crystal particles are oxides, the firing temperature required for sintering is extremely high, and the substrate materials that can be used are inexpensive materials such as platinum plates, which require high heat resistance (
glass plates, etc.) cannot be used. Here, it is possible to disperse or dissolve a binder material such as paraffin in the above dispersion liquid in advance, but if the viscosity of the liquid is high,
The above-mentioned electrophoresis and orientation become difficult, and when glass particles or the like are dispersed, the packing density of the pyroelectric crystal particles during lamination is reduced.

Therefore, in the present invention, a composite pyroelectric material is manufactured by impregnating the polycrystalline pyroelectric material obtained as described above with a binder as a binder afterwards. As described above, thermoplastic organic materials such as paraffin, polymerizable curable organic materials such as epoxy adhesives, etc. can be used as this binder.

Preferred embodiments of the present invention will be described below. First, as a first embodiment of the present invention, a pyroelectric crystal material used as a raw material is given a strong A method of manufacturing a composite pyroelectric material by obtaining a polar-oriented polycrystalline pyroelectric material using L LN b Os, which is a dielectric crystal, and then impregnating it with the binder described above will be described.

A single crystal of LLNb Os was crushed into powder in a mortar, and the powder was separated by sedimentation in ethanol to form a powder with a size of about 1 μm.
& Obtain L=Nb03 powder consisting only of the following particles. These powder particles are dispersed as the dispersed particles in the dispersion liquid, but since trichlorethylene is used as the dispersion liquid, it is necessary to surface-treat the particle surface of the LLNb03 powder to make it lipophilic. That is,
The above powder is mixed in toluene to which a silane coupling agent (for example, 5z-6070 manufactured by Toray Silicone Co., Ltd.) has been added, and the mixture is thoroughly stirred by applying ultrasonic waves, and then mixed using a centrifuge. The powder was collected, washed thoroughly with toluene, and then dried using a hot air dryer. LLNb surface treated in this way
The Os powder particles were sufficiently dispersed in trichlorethylene as the dispersion liquid while applying ultrasonic waves. The LLNb Os particles in this trichlorethylene have a negative charge.

A container 11 shown in FIG. 3 is filled with a dispersion liquid 12 in which the LLNbOs powder particles are dispersed in trichlorethylene.
Two electrode plates 13 and 14 facing each other are arranged horizontally. These electrode plates 13, 14 are formed by depositing conductive NESA films (S, O2 films) 15, 16 on the surfaces of the glass plates 13a, 14a, particularly on the opposing surfaces. These electrode plates 13, 14 are supported in the horizontal direction by electrode support columns 17 made of Teflon or the like, and electrical connection fittings 13b,
It is electrically connected to the DC power supply 18 via 14b and lead wires. Here, the electrode plate 13 in the upper part of the figure is arranged near the liquid level in the dispersion liquid 12, and the vicinity of the electrode plate 13 is cooled by the heat of vaporization due to evaporation at this liquid level.

This electrode plate 13 is set as the positive electrode side (anode side), and a voltage of about 5 KV is applied between both electrodes. At this time, the positive electrode plate 13
1 LiNb□ on the surface of the NESA film 15.

As the particles adhere and stack, the temperature of the LLNb Os particles is lowered near the electrode plate 13 by the cooling effect of the evaporation of trichlorethylene on the liquid surface, and an apparent electric dipole as described above appears. The pyroelectric axis is oriented including the polarity by the electric field between the above electrodes (polar orientation)
be done.

In this way, the LLNbOs particle layer 21 adhered and laminated with polar orientation on the surface facing the electrode plate 130 is deposited on the electrode plate 130.
If it is gently removed from the solution and dried, a polar-oriented polycrystalline pyroelectric material can be obtained. Since the surface of the crystal particles of this polycrystalline pyroelectric material is lipophilic, for example, an oil-based solvent in which polymers such as melted paraffin or transparent lacquer paint diluted with simbu can be easily penetrated into the gaps between the particles. It penetrates and becomes a binder that binds between crystal grains and between grains and the substrate, making it possible to obtain a composite pyroelectric material. In addition, by heat-treating the polycrystalline pyroelectric material taken out from the above liquid at, for example, about 500°C, LLNbOa
The silane coupling agent on the surface of the crystal particles decomposes and evaporates.9
The particle surface becomes hydrophilic.

After making the surface hydrophilic in this way, a composite pyroelectric material can also be obtained by impregnating the polyvinyl alcohol (so-called PVA) aqueous solution into the polycrystalline pyroelectric material and drying it.

Next, FIG. 4 shows the composite pyroelectric material 2 obtained in this way.
1 shows an example of an apparatus for testing the pyroelectric effect of No. 1. In FIG. 4, light from a light source 23 such as an incandescent lamp or an infrared lamp is focused by a lens 24 and irradiated onto a point Q on the surface of the pyroelectric body 21, thereby increasing the temperature of this point Q. ing.

Then, between the lens 24 and the pyroelectric body 21, an aperture window 2 is provided.
A rotating disk 25 having a diameter of 6 is disposed as a light shutter,
By rotating this rotary disk 25 with the rotation of the shaft 27, the irradiation and blocking of light to the point Q is controlled to change the temperature. At the point Q of the composite pyroelectric material 21, an electrode 22 having a diameter of approximately 2 dia is provided by adhering silver paste, for example, and this electrode 22 is electrically connected to one end of the high-sensitivity ammeter 28 via a lead wire or the like. is connected to. Also, lead wires are drawn out from the back side of the composite pyroelectric material 21, for example, from the Nesa film 15,
It is electrically connected to the other end of the high-sensitivity ammeter 28.

The current obtained from the high-sensitivity ammeter 28 after driving the rotary disk 25 one rotation in such a test apparatus is as shown in FIG. 5, for example. In this FIG. 5, light source 2
3 is irradiated to the point Q through the aperture window 26. The time T during which the light is blocked by the disk 25 while N is heated. It is clear that the FF corresponds to the temperature decreasing state, and a pyroelectric effect is obtained.

As explained in conjunction with Figure 3, in the case of a pyroelectric material obtained by electrophoretic electrodeposition while applying a uniform temperature change, a uniform pyroelectric effect can be obtained over the entire area. On the other hand, if the temperature change is not uniform as shown in Figure 2, the pyroelectric effect will vary depending on the location due to only local orientation, making it impossible to obtain a practical pyroelectric material. this is,
It is thought that the local temperature rise occurred due to the application of ultrasonic waves to disperse the pyroelectric crystal particles in the liquid.

Next, a second embodiment of the present invention will be described with reference to FIG.

In FIG. 6, a dispersion liquid 12 in which L↓Nb Os powder particles are dispersed in trichlorethylene is contained in a container 11.
is satisfied and the two electrode plates 13 and 14 are arranged facing each other in the vertical direction in the figure, which is the same as the example shown in FIG. 3 described above. In the embodiment, a heating element 3 such as a heater coil is placed near the electrode plate 13 in the upper part of the figure.
Further, two electrode plates 13 and 14 made of, for example, Teflon material are supported by a rotary table 33, and a pulley 34 connected to the shaft of this rotary table 33 is rotationally driven by a motor 35. It is configured as follows.

In this way, when heating is performed at the upper part of the dispersion liquid 12, so-called liquid convection phenomenon does not occur, and a substantially uniform temperature distribution is created in which the liquid temperature increases from the lower part of the liquid to the upper part. is obtained. Therefore, due to the electric field between the opposing electrodes, as the LbNbOs powder particles move (electrophoresis) to the upper electrode plate 13, the temperature rises, and the particles are polarized by an apparent electric dipole due to the pyroelectric effect. Nesa membrane 1
5 is adhered and laminated on the surface of 5. Of course, the direction of polar orientation (polarity) at this time is opposite to that in the case of FIG. 3 described above (when the temperature is lowered).

That is, in the second embodiment shown in FIG. 6, the electrode plate 13 on the side on which the pyroelectric material is electrodeposited (positive electrode side) is arranged at the upper part in the direction of gravity (that is, the Nesa film serving as the opposing surface After both electrode plates 13 and 14 are submerged in the dispersion liquid 12 in a state in which the electrodes 15 and 15 are facing downward, a voltage of about 5 KV DC is applied between the two electrodes, and the heating element 31 is used to heat only the vicinity of the electrode plate 13. Heat. Then, after a predetermined period of time (for example, about 10 minutes) has passed, most of the LLNbOs particles are removed from the electrode plate 13.
After stacking the electrodes on the Nesa membrane 15, the rotary table 33 is slowly rotated while both electrodes are submerged in the dispersion liquid 12 while the DC voltage is still applied. The rotation is stopped at a position where the opposing surface faces upward. Next, the DC voltage is turned off, and both electrode plates 13
．． 14 along with the rotary table 33, the electrodeposited particle layer on the electrode plate 13 can be taken out of the liquid without falling off. Further, during the above-mentioned pulling, the above-mentioned DC voltage may remain applied. In this case, since the opposing electrode plate 14 comes out of the liquid first, a substantial electric field is then applied to the particles. It is believed that no electrostatic force is applied to the layer and therefore no electrostatic force is applied to the particle layer when the electrode plate 13 exits the liquid.

A composite pyroelectric material can be obtained by impregnating the thus obtained polycrystalline pyroelectric material with a binder in the same manner as in the first embodiment described above.

It goes without saying that the atomization method described above may be used in the steps up to obtaining the polycrystalline pyroelectric material in these first and second embodiments.

Next, as a third embodiment of the present invention, a polycrystalline pyroelectric material is obtained by a fog method, and after impregnated with a mixed substance that becomes glass by heating, a composite pyroelectric material is manufactured by heat treatment. This section explains how to do this.

First, a LLNbOs crystal was used as the pyroelectric crystal, and the same procedures as in the first and second embodiments were carried out by crushing, sedimentation, and separation.
LLNbOs powder particles are obtained by performing surface lipophilic treatment using a silane force and a bubbling agent.

This is sufficiently dispersed in a liquid such as trichlorethylene while applying ultrasonic waves to form a colloidal liquid. For example, about 0.1% by weight (solid) paraffin may be added in advance to this trichlorethylene. Next, as shown in FIG.
A substrate 43 which also serves as an electrode is placed on this quartz plate 42. This substrate 43 has a transparent conductive NESA film CS, O2 film) 45' deposited on one surface of a glass plate 43a. For example, wire mesh electrodes 46 are disposed at positions facing each other, and a DC power source 48 is inserted and connected between the electrodes of the Nesa membrane 45 and the wire mesh electrodes 46. Then, a DC voltage of about 2 KV, for example, is applied between these electrodes to form an electric field, and the colloidal liquid is atomized through the spray nozzle 47 into the space where this electric field is formed. Here, in FIG. 7, the spout of the spray nozzle 47 is arranged outside the wire mesh electrode 46, but the jet nozzle is arranged between the wire mesh electrode 46 and the Nesa membrane electrode 45. Good too.

In the colloidal liquid spouted from the spray nozzle 47 in this way, the Li and NbO5 powder particles, which are dispersed particles, are cooled by the heat of vaporization during atomization of trichlorethylene, and the colloidal liquid is sprayed onto the Nesa film 45 of the substrate 43. When the temperature reaches the temperature, the lychlorethylene is evaporated (by the heating of the heating table 11), the heat of vaporization is taken away, and it is cooled. That is, the heating table 11 is
For example, it is provided to evaporate trichlorethylene by heating to about 200°C'), L=NbOs
Powder particles are constantly subjected to temperature changes. During this temperature drop, an electric dipole appears in each LLNb Oa powder particle due to the pyroelectric effect described above, and while the pyroelectric axis is oriented including the polarity (polar orientation) by the electric field, the NESA film 15 of the substrate 13 is oriented. layered on top. Then, when the thickness of the laminated particle layer reaches, for example, about 0.2 m, the atomization may be stopped, and the entire substrate 13 may be taken out after cooling.

The orientation of the pyroelectric axis in this example is considered to be due to the following effect. That is, the colloidal liquid cloud particles contain a large number of LjNb Os crystal particles at the time of atomization, but due to the subsequent evaporation of trichlorethylene,
Since the crystal particles are rapidly cooled by the heat of vaporization, each of the crystal particles has an electric dipole corresponding to the pyroelectric axis within the liquid droplet due to the pyroelectric effect. As this becomes oriented under the applied electric field, the trichlorethylene liquid evaporates and each cloud droplet becomes oriented with L
Secondary particles consisting of LNb03 particles are layered on the substrate electrode.

Next, as the binder, a solution of a mixed substance that will eventually form a glass composition upon heating is used.

This solution contains, for example, boric anhydride (B203)...3.48 flead acetate...1 B, 96 f(pb (CH
3CO Since it is lipophilic, it is heat-treated at, for example, about 450° C. to decompose and evaporate the silane coupling agent and make the surface hydrophilic, and then it is sufficiently impregnated with the mixed aqueous solution. After air drying, the LLNbOs crystal particle layer is glass-fused by heating at about 480°C for 30 minutes in an electric furnace, for example, to obtain a composite pyroelectric material with strong bonding strength. It will be done. Even with this reinforcement by glass fusion, no particular deterioration of the pyroelectric properties was observed.

According to this third embodiment, when impregnating a colloidal liquid in which glass particles are dispersed, the glass particles close the gaps in the crystal particle layer, making it impossible to sufficiently penetrate into the interior. As a result, a homogeneous glass material can be impregnated without inclusion of air bubbles, etc., and a composite pyroelectric material having a high packing density of pyroelectric crystal particles and excellent pyroelectric properties can be manufactured.

Of course, the polycrystalline pyroelectric material used in this third embodiment may be obtained by the electrophoretic electrodeposition method described above. In addition, as a binder, in addition to the mixed solution that forms the above-mentioned lead borate glass composition when heated, examples of binders include zinc borate, basium borate, alkali aluminum phosphate, and alkali lead silicate. It is also possible to use a mixed solution that forms glass.

Furthermore, it has been confirmed that adding a small amount of ethyl alcohol, soap, etc. to the aqueous solution makes it easier for the aqueous solution to penetrate into the crystal particle layer.

Furthermore, although a spray nozzle was used to atomize the colloidal liquid, an ultrasonic atomizing device (so-called humidifier) may be used instead. Time-stable atomization becomes possible, and a polar-oriented LLNbOs particle layer with good homogeneity can be obtained.

In addition, as for the temperature change given to the particles, instead of the temperature drop change due to the heat of vaporization, a temperature increase change may be given.

[Brief explanation of the drawing]

Figures 1A and B are schematic explanatory diagrams for explaining the pyroelectric effect, Figure 2 is a schematic cross-sectional diagram for explaining the electrophoretic electrodeposition method, and Figure 3 is a first embodiment of the present invention. 4 is a schematic sectional view showing an example of a pyroelectric testing device; FIG. 5 is a time chart showing an example of a current signal obtained by the device shown in FIG. 4; FIG. The figure is a sectional view for explaining the second embodiment of the invention, and FIG. 7 is a sectional view for explaining the third embodiment of the invention. 1... Pyroelectric crystal particles 2... Dispersion liquid 3.4, 13, 14... Fist electrode plate 15.16, 45... Nesa membrane 18.48... DC power supply 21... Electric Adhesive particle layer 31, fist, heating element 43...electrode substrate 46...wire mesh electrode 47...spray nozzle patent applicant Sony Corporation representative patent attorney Kodo Koike 1) Sakae Mura -114
ρ 5th s + W & 6th period 7am

Claims (1)

[Claims] A composite pyroelectric material comprising the steps of: obtaining a polycrystalline pyroelectric layer by laminating pyroelectric crystal particles on a substrate with the pyroelectric axis oriented; and impregnating the polycrystalline pyroelectric layer with a binder. Electrical body manufacturing method.