JPS6266689A - Manufacture of composite sheet with piezoelectric or pyroelectric property - Google Patents

Abstract

PURPOSE:To obtain a composite piezoelectric or pyroelectric sheet having high sensitivity, excellent primary workability by dispersing and solidifying particles of piezoelectric or pyroelectric sintered material on insulating polymer with which is uniformly coated a smooth carrier to form a sole layer, then removing skin layers, forming both electrodes on both side surfaces, and polarizing the electrodes. CONSTITUTION:Particles of piezoelectric or pyroelectric sintered material (e.g., sintered material of titanium lead zirconate) are pulverized and screened. A coating film 1 of solution of heat resistant thermosetting resin (e.g., polyamide resin) is formed of a knife coater on one side surface of an aluminum foil 3. The particles 4 are uniformly dispersed so as not to superpose (in dispersing density of 80-90 particles/m<2>). After the film 1 is solidified, the film is dipped in an aqueous ferric chloride bath to be etched, dried, and thermally cured by a flat plate press. The film is then polished with a sandpaper to expose the particles. Thin copper films are formed on both side surfaces by sputtering as electrodes. A voltage is applied between the electrodes to be polarized to obtain a composite sheet.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention provides a piezoelectric material having a dispersed structure in which piezoelectric or pyroelectric sintered particles are bonded in parallel in a single layer in an insulating polymer. Alternatively, the present invention relates to a method for easily and accurately manufacturing a composite sheet having pyroelectric properties.

A composite sheet having piezoelectric or pyroelectric properties obtained by the method of the present invention can be made into a highly sensitive pressure-sensitive or heat-sensitive sensor by combining it with a suitable first-stage amplifier. Furthermore, it can be an actuator or a vibrating body that is driven by applying a voltage from the outside.

[Prior art]

Previous attempts have been made to obtain composite sheets with excellent flexibility and workability, in which particles obtained by crushing piezoelectric or pyroelectric sintered bodies are dispersed in an insulating polymer (hereinafter referred to as a binder). It has been done.

The conventional method for manufacturing composite sheets was to knead particles and a binder and form a sheet using an extruder or the like.

Composite sheets produced by this method had extremely poor piezoelectric sensitivity or pyroelectric sensitivity for the following reasons.

(1) Each of the particles in the composite sheet is coated with a binder, and there are almost no or very few particles in direct contact with the electrodes provided on both sides of the composite sheet.

(II) The specific electric constant of the binder is relatively small, whereas the specific dielectric constant of the particles is extremely large. When attempting to polarize a composite sheet by applying a voltage between the electrodes to provide the electric field strength necessary to polarize the particles, an electric field is also formed in the binder interposed between the electrodes and the particles.

That is, the particles and the binder are coupled in series between the electrodes, and the ratio of the electric field strength of the particles to the electric field strength of the binder is equal to the ratio of the reciprocals of their respective dielectric constants.

The dielectric constant of piezoelectric or pyroelectric sintered particles is usually 1
00 to several 1ooo, while the relative permittivity of the binder is 3 to
It is 10.

For example, the electric field strength required to polarize particles is 6KV/w.
As, the binder must be given an electrolytic strength several ten to several thousand times that strength, and if such a strong electric field is applied, the binder will be destroyed.

Therefore, a voltage can only be applied within the withstand voltage limit of the binder, and at these voltages the binder consumes the voltage and cannot sufficiently polarize the particles. Conventional methods for manufacturing composite sheets only yield particles and binders bonded in series, and even if the number of particles is increased, the piezoelectric or pyroelectric properties of the particles themselves1, ,. There were difficulties in 1 and 8.

For these reasons, it has not been put into practical use even though it has the advantages of flexibility and workability.

A desirable structure of the composite sheet is that piezoelectric particles or pyroelectric sintered particles are arranged in parallel with the binder. Squid 4 car. . □ゎE□yo i Full. 1
゜t It is desirable to have a tie.

With such a structure, the voltage applied between the electrodes is directly applied to the particles to form an electric field, and the purpose can be sufficiently achieved with a voltage that does not affect the binder.

Conventionally, the method for manufacturing a composite sheet with such a structure is to form a piezoelectric or pyroelectric sintered body into rod shapes, arrange them in parallel, and fix them with a bonding agent to form rod-shaped sheets. or make the sintered body into a thick plate shape, make deep grooves vertically and horizontally, put a binder in the grooves and fix it to make it into a rod shape, and make these rod-shaped objects. Methods of manufacturing composite sheets by slicing them thinly have been proposed, but these sintered bodies are extremely hard and difficult to cut into thin sheets (thin sheets), so they have not been put to practical use. 0 [Object of the invention] The present invention has a dispersed structure in which piezoelectric or pyroelectric sintered particles are bonded in parallel in a single layer in a binder, which has high sensitivity and has secondary An object of the present invention is to provide a method for easily and economically producing a piezoelectric or pyroelectric composite sheet with excellent processability.

[Structure of the invention]

The present invention comprises the steps of obtaining a film in which particles of a piezoelectric or pyroelectric sintered body are dispersed in a single layer in a binder, removing the skin layer on both sides of the film to expose each particle, and This method of manufacturing a composite sheet is characterized in that it comprises a step of forming electrodes on both sides and applying a voltage to polarize the sheet. More specifically, a coating film of a heat-resistant liquid thermoplastic resin or thermosetting resin (binder) is formed on a carrier, and a piezoelectric or pyroelectric sintered body is formed on this coating film. The particle size is 148 μrr1 when sieved using an ASTM standard sieve.
A step of dropping particles in the range of 2Cμm stop using a sieve or the like to form a single layer of particles along the interface with the carrier in the coating film, and drying and preliminarily solidifying or After curing and removing the carrier, the film is sandwiched between plates and heated and pressurized or fully irradiated with radiation to complete assimilation or curing. The skin layers on both sides of the film, in which the obtained particles form a single layer, are sanded with R-NO? -1 Remove by polishing or etching using a surface grinder or sandblasting method. In the step of removing the skin N, the sum A of the projected area of each particle from the perpendicular direction of the film, and the sum B of the surface structure of the exposed portion on the front or back surface, are calculated as follows:
Each epidermis is removed until A≧0.5.

In this step, it is desirable that both the particle portion and the binder be polished or etched in order to obtain a smooth film. Gold, silver, copper, aluminum, etc. are vacuum deposited on both sides of the film where the resulting particles are exposed.
This is a method in which an electrode is formed by ion blating or a cross-zeta ring method, and a voltage is applied to the electrode to polarize it to obtain a piezoelectric or pyroelectric composite sheet.

The pressure t or pyroelectric sintered body used in the present invention is a sintered body in which crystals already have spontaneous polarization in a state where no electric field or external force is applied.

Examples of such materials include barium titanate having an R-lobskite crystal structure, modified titanium lead, titanium-enriched lead zirconate and its modified products, and numerous sintered bodies made from tantalates, etc. It will be done. In addition, as a method of pulverizing the material, use the entire flux which has been pulverized by mechanical or thermal punching, etc., and classified according to the intended use and the thickness of the composite sheet. Rounding the particles by a process such as a ball mill before they are classified will make the dispersion uniform in the later process, and will also improve the affinity between the particles and the binder, which will prevent the formation of voids in the binder. It becomes less. The particles immediately after being mechanically crushed are Wadeu's Round Ind.
ex (J, G=o740p443~451 (19
32) Wade's t, H) is 0.01 or less, but it is desirable that the Round Index of the particles used in the present invention is larger, and if it is 02 or more, the effect will be recognized.

A piezoelectric or pyroelectric sintered body is a structure made up of microcrystals, and generally there are defects such as voids inside the sintered body, and the withstand voltage depends on these defects. Indicates a higher value if absent. When this sintered body is crushed into fine particles, most of the O defects such as voids are released on the crushed surface, and the number of defects decreases as the particle size becomes smaller.

That is, it is desirable to make the particles as fine as possible without causing any problems in manufacturing the composite sort.

Practically speaking, the particle size used is preferably in the range of 148 μm/' and 20 μm stop when sieved using an ASTM standard sieve. Furthermore, it is desirable that the thickness be in the range of 53 μm-ξ and 20 μm stop.

If the grain size is 148 μm pass, the number of defects such as voids within the grains per unit volume will be reduced, and the effect of this will begin to appear in the improvement of withstand voltage. Further, if the thickness is about 53 μm, a withstand voltage of 50% or more of the electric field strength required for polarization is maintained.

On the other hand, if it is less than 20 μm, the processability of the film will be poor, and if the particles are exposed on both sides, it will be extremely thin and the strength of the composite sheet will be weak, making it difficult to handle.

The bond used in the present invention may be any material as long as it has heat resistance and insulation properties and can hold the particles of the sintered body, such as thermoplastic resins such as pyriethersulfone, polycarbonate, +p IJ imide, pyri, etc. amide imide,
Thermosetting resins such as epoxy resins and modified resins thereof are preferred.

In order to form a film in which the particles are dispersed in a single layer, it is also desirable to take appropriate measures such as coating a release agent on a flat plate serving as a carrier.

Next, the surface layer of the obtained film is removed until each particle edge is exposed on both sides of the film, for example, by polishing with a sand dA-, surface grinding with a surface grinder, or by spraying abrasive grains to the surface. Mechanical means such as abrasive sandblasting or liquid honing, or chemical etching of the binder (for example, etching with an aqueous hydrazine solution for pyriimide resins) can be applied. When removing the surface layer of the film, there is no problem even if the surface of the particles is scraped off at the same time. , care must be taken to avoid pinholes or damage to the bonding agent.

In the present invention, the step of exposing the edges of each particle on both sides of the film is particularly important, so that the surface of the exposed particles does not change in quality or become contaminated with other substances before proceeding to the next step. It is necessary to The larger the surface area of the particles exposed in this way, the more the polarization effect acts on the entire particle and the piezoelectricity or pyroelectricity can be improved.

The ratio B/A of the sum B of the exposed area of each of the front and back surfaces to the sum A of the projected "area of the particles contained in the film in the vertical direction" represents the exposed area, and B/A is 0.5. It is more preferably 0.75 or more.

To measure B/A, use the difference in visible light transmittance between the particles and the binder, as shown in Figure 2, use transmitted light to determine the projected area, and use all surface reflected light to determine the exposed area. required by doing.

In the present invention, conventional dry or wet surface metallization techniques can be applied to form electrodes on both sides of the film where the core particles are exposed.

For example, the electrodes may be formed using gold, silver, copper, aluminum, or the like by snow ξ sintering, vacuum deposition, or ion silating, or may be formed using electroless plating or conductive paint. Furthermore, these may be combined.

Subsequently, polarization in the present invention is performed by a conventional method, and a voltage is applied after confirming that the electrodes formed on both sides are not short-circuited. The voltage to be applied varies depending on the type of piezoelectric or pyroelectric sintered body used, but the voltage required to polarize the sintered body (electric field strength x thickness of the sintered body) is applied. This is sufficient.

For example, lead zirconate titanate (Tohoku Metal Industry NEPE)
The electric field required for polarization of the sintered body of C■N21) is 6, V
/ tan If the thickness of a composite sheet using particles of the sintered body is 50 μm, then 0.3 (6KV/m
0.05 rran) KV. If dariimide resin is used as a binder, the withstand voltage of pyriimide resin is 10 KV/original or more, and it is possible to polarize without being damaged.

〔Effect of the invention〕

The manufacturing method of the present invention is suitable as an industrial manufacturing method because a composite sheet with excellent piezoelectricity or pyroelectricity, good workability, and high flexibility can be obtained easily and economically.

The piezoelectric or pyroelectric composite sheet manufactured in this way can be used as a piezoelectric sensor for sensing external pressure, or as a temperature sensor for sensing temporal fluctuations in temperature, in accordance with the conventional uses of the sintered body itself. , or as an infrared sensing sensor.

Furthermore, compared to conventional sheets made of sintered bodies, the composite sheet of the present invention has a sensor area several ten times larger, and from this point as well, the sensitivity can be improved.

Example 1 A sintered body of lead zirconate titanate (NEPEC N21 manufactured by Tohoku Metal Industry Co., Ltd.) was used as a piezoelectric or pyroelectric sintered body particle.
The crushed grains (hereinafter referred to as N21) were treated in a 10 cm diameter bit with mixed alumina ceramic balls of 6 m diameter and 2 cm diameter at 105 revolutions per minute for 50 hours, and then sieved and passed the ASTM standard. Aperture 37μ with standard sieve
A particle size of 20 μm stop was used. The average roundness of Widell was 0.2. A coating film of the binder solution was applied to one side of the aluminum foil using a knife coater, and the 9N21 particles were sieved from the top first and spread uniformly so that the particles did not overlap vertically. The thickness of the coating film at this time was approximately 20 μm after drying. The binder is pyriamideimide resin, which is a heat-resistant thermosetting resin, and its solution (AI'7 manufactured by Furukawa Electric Co., Ltd.) is used as a binder.
A 22% by weight resin-containing needle of varnish ((dissolved in N-methylpyrrolidone solvent naphtha mixed solvent)) (hereinafter referred to as AI fest) was used as a raw material. Further, the concentration of N21 particles was set to 80 to 90 particles per wn.

The solvent was sufficiently removed in a vacuum dryer at 40° C. to solidify the coating film. Subsequently, the aluminum foil was etched out by immersing it in an aqueous ferric chloride solution to obtain a film 7t in which N21 particles were dispersed in a single layer. Furthermore, after drying at 80°C for 60 minutes, it was heated and cured at 200°C for 30 minutes using a flat plate press. Next, SandE ξ- with a particle size of LOOO to L500 was used to expose most of the particles on both sides of the film. Polishing was performed until the degree of particle exposure (B/A) was 0.80.

The thickness was 16±4 μm. As electrodes, copper thin films with a thickness of 1 μm were formed on both sides of the film by snow ξ tuttering. A DC voltage of 96 cm was applied at room temperature between the electrodes formed on both sides of the film.
wott (average electric field strength 6 KV/rran)
was applied for 15 minutes to polarize the film and create a composite sheet.

A composite sheet with extremely good piezoelectricity and pyroelectricity was obtained. This composite sheet had good heat resistance, and the lead wires could be connected to the electrodes by soldering. Other properties are shown in Table 1.

Example 2 N21 particle size is 148 μm/”?s, 120 μm
A composite sheet was produced using exactly the same process and conditions as in Example 1, except that the solution was m-stop and the thickness of the coating film of the solution was adjusted to be approximately 70 μm after drying.

A composite sheet with good piezoelectricity and pyroelectricity was obtained, and its properties are shown in Table 1.

Example 3 A composite sheet was produced using the same steps and conditions as in Example 1, except that the N21 particles were polished until the degree of exposure (B/A) was 0.60. This composite sheet had good piezoelectricity and pyroelectricity, and these properties are shown in Table 1. These tend to be lower than the characteristics of Example 1 or 2.

Example 4 A heat-resistant thermoplastic resin (N') ethersulfone (UCC, hereinafter referred to as PES) in N-methylpyrrolidone solution (resin content: 22% by weight) was used as a binder. Proceeding with the same process and conditions, a composite track was created. Lead wire connections to this composite sheet were made using conductive paste.

Its piezoelectricity and pyroelectricity are very good, and these properties are shown in Table 1.

Example 5 A film in which N21 particles obtained in Example 1 were dispersed in a single layer was fixed on a suction plate installed on a surface grinder,
A composite sheet was produced using the same process and conditions as in Example 1, except that a grinder with a finishing accuracy of 1 μm was used to grind each side one by one. As a result, the properties of this composite sheet were similar to those of Example 1, but the working time required to achieve the same exposure degree (B/A) was as in Example 1.
It was shortened to about 1/3 of that time.

Example 6 A composite sheet was produced using the same process and conditions as in Example 1, except that a thin silver film with a thickness of 1 μm was formed on both sides of the film using a vacuum deposition method instead of sputtering. The lead wires were connected to this composite sheet using a conductor. This composite notebook had good piezoelectricity and pyroelectricity, and its characteristics are shown in Table 1.

Example 7 The sintered body used was calcium titanate modified lead titanate (
N200 is a material with pyroelectric properties, NE manufactured by Tohoku Metal Industry Co., Ltd.
A composite sheet was produced using the same process and conditions as in Example 1, except that PEC N200 (hereinafter referred to as N200) was used. Although the piezoelectricity of this composite sheet is slightly lower than that of N200 alone, it has very good pyroelectricity, and its properties are shown in Table 1.

Example 8 N21 particles have an average roundness of Wide// of 0
．． A composite sheet was prepared in exactly the same manner as in Example 1 except for the other steps 4. Its properties are shown in Table 1.

Comparative Example 1 The particle size of N21 is 17711 mF, 149
A composite sheet was produced using the same process and conditions as in Example 1, except that the μm stop was used. As a result, damage due to dielectric breakdown occurred in 4 out of 10 sheets during the polarization process.

Comparative Example 2 Ten composite sheets were prepared according to Example 1 except that fine N21 particles with a size of 20 μm were used, but the exposure degree (B/A) was 0. The composite sheet was damaged before it reached 1 or more, and no finished product could be obtained.

Comparative Example 3 The exposure degree (B/A) of N21 particles was less than O11, and the outside of the fish was left almost unexposed as in Example 1.
A composite sheet was created using the same process.

As shown in Table 1, its piezoelectricity and pyroelectricity were both at low levels.

Comparative Example 4 N21 particles of 20 μm x used in Comparative Example 2 and A■
The mixture was kneaded at a weight ratio of 8:1 with Fes, coated on an aluminum foil carrier, and dried. After the aluminum foil was chemically etched away, it was heated at 80° C. for 30 minutes. This is done in a flat plate press for 2
It was heated and cured at 00°C for 30 minutes.

Next, a 1 μm thick copper thin film was applied to both sides using S) F tuttering. This was carried out at room temperature, average electrolytic strength 12KV/m+, 15
A composite sheet was created by polarization under conditions of 1 minute.

As shown in Table 1, its piezoelectricity and pyroelectricity were both at low levels.

Comparative Example 5 A composite sheet was prepared in exactly the same manner as in Example 1, except that N21 particles were not subjected to a ball milling process and had an average Wi de It roundness of 01 or less. As a result, in the polarization process, 7 out of 10
Damage occurred due to dielectric breakdown.

This dielectric breakdown is thought to be caused by minute air bubbles generated between the particle surface and the binder surface because the roundness of the particles is small.

Comparative Example 6 N21 sintered block was cut to a thickness of 10 mm using a diamond cutting saw.
It was cut out to 0 μm. Next, apply 1μ on both sides with Snow Z Tsutaring.
A thin copper film of m thickness was applied. This was polarized in insulating oil for a room temperature transformer at an average electrolytic strength of 4 KV/mm for 15 minutes to produce a sintered sheet. The properties are shown in Table 1.

Comparative Example 7 N200 sintered block was cut to a thickness of 1 with a diamond saw
It was cut out at 0011m. Next, a 111 m thick copper thin film was applied to both sides by sputtering. This is an average electrolytic strength of 4 KV/ms in transformer insulating oil at 1180°C.
Polarization was performed for 15 minutes to create a sintered sheet. The properties are shown in Table 1.

(1) VB: Dielectric strength voltage (in insulating oil for transformer at 180°C) (2) εr: Relative dielectric constant (l KHz) (3)
d3. : Piezoelectric constant (Z-X, 10Hz) (4) λ: Pyroelectric constant (5) RV : Optical Re5ponsivity (chopping frequency 8Hz, light-receiving surface blackening treatment, sample area 1M
)

[Brief explanation of drawings]

FIG. 1 shows a method for obtaining a film in which piezoelectric or pyroelectric sintered particles of the present invention are dispersed in a single layer in a binder. Figure 2 shows a model of a microscopic photograph in which the skin layers on both sides of the film have been removed to expose the particles. ). 2 in FIG. 2 is an observation of the exposed portion with reflected light, and is used to determine the sum B of the area of the exposed portion of the particles. In the figure, 1 is a liquid binder (insulating polymer), 2 is a sweeper 3, a carrier 4 is a piezoelectric or pyroelectric sintered body, and 5 is a cross section of a film in which particles are dispersed in a single layer.

Claims (4)

[Claims] (1) In a method for manufacturing a piezoelectric or pyroelectric composite sheet in which particles of a piezoelectric or pyroelectric sintered body are dispersed in a single layer in an insulating polymer and are in direct contact with double-sided electrodes, a liquid An insulating polymer is coated to a uniform thickness on a carrier with a smooth surface, particles of a piezoelectric or pyroelectric sintered body are scattered on the insulating polymer to form a single layer, and then Step (I) of curing or solidifying the insulating polymer to obtain a film having a single layer of piezoelectric or pyroelectric sintered particles.
Step (II) of removing the skin layer from both sides of the obtained film by mechanical or chemical means to expose particles of the piezoelectric or pyroelectric sintered body dispersed in a single layer on both sides of the film (II ) and a step (III) of forming electrodes on both sides of the film and applying a voltage to polarize the film. A piezoelectric or pyroelectric composite sheet in which the electrodes and the particles are in direct contact with each other. manufacturing method. (2) The particle size of the piezoelectric or pyroelectric sintered body is 14
The method for manufacturing a composite sheet according to claim 1, which is a sieve of 8 μm pass and 20 μm stop (ASTM standard sieve). (3) The shape of the particles of the piezoelectric or pyroelectric sintered body is Wad.
Claim 1 in which the roundness of ell is 0.2 or more
2. A method for producing a composite sheet according to item 2. (4) The degree of exposure of the particles of the piezoelectric or pyroelectric sintered body exposed on the surface of the film is the sum of the vertical projected areas of each particle A
In contrast, when the ratio B/A of the sum B of the exposed areas of each surface is 0.
4. The method for manufacturing a composite sheet according to claims 1 to 3, wherein the skin layer is removed by polishing or etching until it becomes 5 or more.