JPH0684409A - Conductive powder, conductive paste and actuator - Google Patents

Abstract

PURPOSE:To reduce a quantity of precious metal used for an electrode, a stacked actuator or the like, and restrain the separation of an electrode layer by using conductive powder comprising a conductive metal sheath layer formed around a piezoelectric or electrostrictive ceramic particle. CONSTITUTION:No specific restriction is imposed on a grain size, but extra fine powder with a grain size of 0.5mum or less can form a uniform precious metal sheath layer. The precious metal in this case is Ag, Pd or the like. Water soluble tetrachloropalladium acid ammonium salt is dissolved in water to prepare primary dispersion solution. Then, water solution of hydrazine as a reducing agent is added to liquid where ceramic powder is dispersed in the water solution of precious metal salt, thereby forming a thin film near a monoatomic film on the surface of ceramic powder. Then, the ceramic powder is taken out and dispersed in liquid containing the precious metal salt and hydroxyethyl cellulose (water soluble polymer). In addition, a reducing agent is added to the liquid. Thereafter, secondary sheathing ceramic powder is taken out from the diffused solution and dried. This powder after mixed with pure precious metal powder, or alone, is used as conductive paste.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive powder. In particular, the present invention relates to a conductive powder that can be advantageously used for manufacturing a piezoelectric or electrostrictive actuator, and a conductive paste containing the conductive powder. The present invention also relates to a piezoelectric or electrostrictive actuator using the above conductive powder.

[0002]

2. Description of the Related Art In recent years, research on the structure of a piezoelectric or electrostrictive element as a positioner and an actuator has been actively conducted. For example, a piezoelectric or electrostrictive element is used as a laminated piezoelectric or electrostrictive actuator having a structure in which an electrode layer is formed on the surface and a large number of layers are laminated. The laminated actuator has a large generation force, a high response speed, and a higher electromechanical conversion efficiency than the bimorph type actuator.
It is incorporated and used as a fine displacement control element in a precision positioning device or the like.

There are two types of manufacturing methods for laminated piezoelectric or electrostrictive actuators. One is to cut and polish a sintered piezoelectric or electrostrictive ceramic into a thin plate shape, apply an electrode to this, and then bond or crimp it to form a laminate, and then laminate the internal electrode on the end face of the laminate. Is a method of attaching end electrodes that are electrically connected every other layer. This manufacturing method has a problem in that the productivity is poor due to the large number of steps, and because the thickness of one piezoelectric or electrostrictive ceramic cannot be made too thin due to processing restrictions, the driving voltage cannot be lowered. Another manufacturing method is almost the same as the manufacturing method of laminated ceramics, and a mixed liquid prepared by mixing a suitable piezoelectric or electrostrictive ceramic powder and a binder with a solvent is used to prepare a doctor blade method, a roll coater method or a screen. A green sheet (unfired dielectric sheet) is formed into a sheet by using a coating method such as a printing method, and then a conductive paste to be an internal electrode is coated on the surface of the green sheet by a method such as printing. After manufacturing the blocks, the blocks are sequentially stacked to obtain a laminated body, the laminated body is fired, and finally, end electrodes for electrically connecting every other internal electrode to the end surface of the fired product are attached. According to this manufacturing method,
There is an advantage that the laminated actuator can be manufactured with high mass productivity and the driving voltage of the obtained laminated actuator can be lowered.

In the latter manufacturing method using a green sheet, as the conductive paste used for forming the internal electrode layer, a conductive metal powder uniformly dispersed in an organic vehicle is used. Become. The conductive metal powder has a melting point equal to or higher than the sintering temperature of the piezoelectric or electrostrictive ceramics used, and even if it is fired in contact with the piezoelectric or electrostrictive ceramics in the air atmosphere,
The condition is that the powder is a metal material that is neither oxidized nor causes a reaction. As a metal powder satisfying this condition, noble metals such as platinum, gold, palladium, silver or alloys thereof have been generally used in the past. However, when firing in a reducing atmosphere or a low oxygen partial pressure atmosphere, nickel, an equivalent base metal, or an alloy containing a base metal may be used.

The manufacturing method using the above green sheet is
As described above, the manufacturing method is highly mass-producible and excellent, but in general, there is an extreme difference in the expansion / contraction curve during firing between the conductive metal material and the piezoelectric or electrostrictive ceramics. When firing a laminate with a coating layer of a hydrophilic metal material (that is, at the time of simultaneous firing) or after firing,
There is a problem that delamination (delamination) is likely to occur at the interface with the conductive metal material layer (electrode layer). When delamination occurs, various properties of the manufactured laminated actuator, especially mechanical strength, are greatly reduced,
Practicality is impaired. Further, even if delamination does not occur, strain is likely to remain after firing, and the strength of the laminated actuator may decrease. Therefore, in the simultaneous firing, it was necessary to set delicate conditions and operate with high skill.

As means for preventing the occurrence of delamination in the above co-firing, piezoelectric or electrostrictive ceramics as the co-material (the same as the piezoelectric or electrostrictive ceramics constituting the green sheet) are used in the conductive metal material coating layer. The method of making the expansion / contraction curve of the metal material layer (electrode layer) closer to the expansion / contraction curve of the green sheet by mixing particles of the material or the ceramic material containing the same component in an amount of several% to several tens%. Has been done. According to this method, it is possible to avoid the occurrence of delamination and residual strain, and further it is possible to reduce the amount of the conductive metal material used in the electrode layer. However, since the piezoelectric or electrostrictive ceramics used as the common material is an insulator, if the amount of common material in the electrode layer is increased so that the occurrence of delamination and the like can be effectively avoided, the electrode layer However, there is a problem that the electrical characteristics of are significantly deteriorated.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a conductive powder and a conductive paste which can be particularly advantageously used for manufacturing a piezoelectric or electrostrictive actuator using a green sheet and utilizing simultaneous firing. To do.

Another object of the present invention is to provide a conductive powder and a conductive paste which can be manufactured at low cost without lowering the electrical characteristics of the electrode layer attached to the piezoelectric or electrostrictive element. is there.

A further object of the present invention is to provide a piezoelectric or electrostrictive actuator having high mechanical and electrical characteristics, particularly a laminated type, which is manufactured by using the electrically conductive powder and the electrically conductive paste having the above excellent characteristics. There is also the provision of an actuator.

[0010]

DISCLOSURE OF THE INVENTION The present invention includes a conductive powder having a conductive metal material coating layer formed around piezoelectric or electrostrictive ceramic particles, and the conductive powder containing the conductive powder. In a conductive paste consisting of.

The present invention also resides in a piezoelectric or electrostrictive actuator having an electrode layer formed of the above-mentioned conductive powder (or conductive paste).

The present invention will now be described in detail with reference to the accompanying drawings showing a typical laminated piezoelectric or electrostrictive actuator. 1 and 2 are schematic views showing an example of the configuration of a typical laminated piezoelectric or electrostrictive actuator (also simply referred to as a laminated actuator in this specification). The structure itself of these laminated actuators is already known and used.

The multilayer actuator shown in FIG. 1 has a structure known and used before, and includes an electrode layer (internal electrode layer) 11 formed of conductive powder and a piezoelectric or electrostrictive ceramic. And the layers 12 to be formed are alternately laminated. External electrodes 13 connected to the internal electrodes on each side are provided on both sides. Although the laminated actuator usually has several tens of electrode layers or more (for example, 100 layers) laminated, the number of layers is reduced for the sake of clarity.

The multi-layer actuator of FIG. 2 is proposed as an improved version of the multi-layer actuator of FIG. 1, and is an electrode layer (internal electrode layer) formed of conductive powder.
21 and layers 22 made of piezoelectric or electrostrictive ceramic are alternately laminated. External electrodes 23 connected to the internal electrodes on each side are provided on both sides. However, like the laminated actuator of FIG.
In order to alternately conduct the internal electrode 21 and the external electrode 23 on both sides, in the type shown in FIG.
An insulator 24 is provided on one side of No. 1 to form an insulating portion. The insulators are provided in alternation, as shown in FIG. In the laminated actuator of the type shown in FIG. 2, the electrode layers are usually laminated by several tens or more layers (for example, hundred layers), but the number of layers is reduced for the sake of clarity.

Next, the conductive powder, which is a characteristic feature of the present invention, will be described in detail. The conductive powder of the present invention is a conductive powder obtained by forming a conductive metal material coating layer around piezoelectric or electrostrictive ceramic particles as described above.

In order to produce the conductive powder of the present invention,
Around the piezoelectric or electrostrictive ceramic particles, a conductive metal material coating layer may be formed using a conventionally known method such as chemical plating or electroless plating.
The conductive powder obtained by such a method is not industrially advantageous because it is difficult to stably obtain desired electrode characteristics when the electrode layer is formed. Therefore, in order to produce the electroconductive powder of the present invention, it is desirable to utilize the following newly developed method for forming a highly pure electroconductive metal material coating layer.

That is, a preferable method for producing a ceramic powder coated with a noble metal is to add a reducing agent to a dispersion liquid (primary dispersion liquid) in which a ceramic powder is dispersed in an aqueous solution of a noble metal salt,
A step of forming a noble metal thin film layer on the surface of the ceramic powder, and the ceramic particles having the noble metal thin film layer are dispersed in an aqueous solution containing a noble metal salt and a water-soluble polymer, and then in the dispersion liquid (secondary dispersion liquid). A method comprising adding a reducing agent to form a noble metal layer around the noble metal thin film layer on the surface of ceramic particles.

The above method can be said to be an improved method of conventional chemical plating. That is, a known chemical plating method in which a reducing agent is added to a dispersion liquid containing a ceramic powder dispersed in an aqueous solution of a noble metal salt to reduce the noble metal salt, and a noble metal is deposited on the surface of the ceramic powder to form a noble metal coating layer. Method of utilizing the method, an improved method of suppressing the agglomeration of ceramic powder or noble metal-coated particles to form a noble metal coating layer having high exposure of the ceramic phase and high purity, that is, containing less ceramic components. Is.

There are no particular restrictions on the material components of the piezoelectric or electrostrictive ceramic particles used in the present invention.
PbTi0 ₃ , PZT (abbreviation of Pb (Zr, Ti) O ₃ ), PLZT (abbreviation of (Pb, La) (Zr, Ti) O ₃ ), or PMN (Pb (Mg _1/3 Nb _2/3 ) O
Piezoelectric or electrostrictive ceramic particle powders such as metal oxides represented by (abbreviation of ₃ ) or particles of metal oxides containing these metal oxides as a main component can be used.

The particle size of the piezoelectric or electrostrictive ceramic particles used in the present invention is not particularly limited, but if the above method is used, the particle size is 3 μm or less, particularly 1 μm or less,
A uniform noble metal coating of ultrafine powder having a particle size of 0.8 μm or less and further a particle size of 0.5 μm or less is realized.

As the noble metal with which the surface of the piezoelectric or electrostrictive ceramic particles is coated, a noble metal having a high electric conductivity such as silver, platinum, palladium or gold is selected.

In the preferred method for producing the above-mentioned noble metal-coated ceramic powder, a noble metal salt is first dissolved in water to prepare an aqueous solution of the noble metal, and then the ceramic powder is uniformly dispersed therein to obtain a primary dispersion liquid. It is also possible to use a method in which an aqueous dispersion of ceramic powder is first prepared and then a water-soluble noble metal salt is dissolved therein. As the water-soluble noble metal salt, various noble metal salts (or complexes) such as tetrachloropalladate ammonium salt, tetraamminepalladium chloride, tetrachloroplatinum ammonium salt, and tetraammineplatinic chloride can be used. It should be noted that a substance other than the water-soluble noble metal salt and the ceramic powder (for example, a water-soluble polymer) may be added to the primary dispersion liquid in a small amount. However, for example, when the water-soluble polymer is added, the addition amount needs to be smaller than the addition amount of the water-soluble polymer to the secondary dispersion liquid described later.

Next, a ceramic dispersion liquid (primary dispersion liquid) obtained by dispersing ceramic powder in the above-mentioned precious metal salt aqueous solution.
A reducing agent is added to this dispersion while stirring. As the reducing agent, a reducing agent such as hydrazine, hydrazine hydrochloride, formic acid, formalin, hypophosphorous acid and the like used in a known chemical plating method is generally used. The reducing agent is usually added as an aqueous solution to the above primary dispersion. Alternatively, the above primary dispersion may be added to the aqueous reducing agent solution. By mixing the primary dispersion and the reducing agent aqueous solution, a noble metal thin film (a monoatomic film or a thin film similar thereto) is formed on the surface of the ceramic powder.

Next, the ceramic powder having a noble metal thin film layer formed on the surface (referred to as a primary coating ceramic powder) is taken out from the dispersion liquid, and this primary coating ceramic powder is then mixed with a precious metal salt and a water-soluble polymer. To prepare a secondary dispersion liquid. However,
The primary coating ceramic powder does not necessarily have to be separated from the primary dispersion, and the noble metal salt and the water-soluble polymer may be added to the primary dispersion containing the primary coating ceramic powder to prepare the secondary dispersion.

The noble metal salt (water-soluble noble metal) used in preparing the secondary dispersion may be the same as the water-soluble noble metal salt used in preparing the primary dispersion, or may be a different water-soluble noble metal salt. It may be.

The water-soluble polymer used for preparing the secondary dispersion is not particularly limited, but as the water-soluble polymer, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, hydroxyethyl methyl cellulose having good dispersibility of fine ceramic powder can be used. It is desirable to use water-soluble cellulose derivatives such as, hydroxypropylmethyl cellulose, carboxymethyl cellulose and the like. However, water-soluble natural product polymers such as gelatin and casein, and water-soluble synthetic polymer compounds such as polyvinyl alcohol and polyvinylpyrrolidone may be used.

Next, a reducing agent is added to this dispersion while stirring the secondary dispersion prepared by dispersing the primary coating ceramic powder in the aqueous solution containing the above-mentioned noble metal salt and water-soluble polymer. As the reducing agent, in principle, the reducing agent used for producing the primary coating ceramic powder is used, but it is not necessary to be the same. By mixing the secondary dispersion and the reducing agent (reducing agent aqueous solution), a noble metal layer much thicker than the primary coating layer is formed on the surface of the primary coating ceramic powder.

Next, the ceramic powder having a noble metal layer laminated on the surface (referred to as a secondary coated ceramic powder) is taken out from the dispersion and dried to obtain the target noble metal coated ceramic powder.

In the electroconductive powder of the present invention in which the electroconductive metal material coating layer is formed around the piezoelectric or electrostrictive ceramic particles, the ceramic portion to be the core portion (nucleus or core) and the coating layer (shell ) Can be arbitrarily selected, but usually ceramic: precious metal is 5:
It is 95 to 99: 1 (weight ratio). However, from 10:90
97: 3 (weight ratio), further 5:95 to 80:20
(Weight ratio) is preferable. In particular, the ceramic: noble metal is preferably 10:90 to 50:50 (weight ratio).

The electrically conductive powder of the present invention can be mixed as it is with an ordinary binder or the like into an electrically conductive coating (paste) according to a conventional method. The electrostrictive ceramic particle powder may be used as a mixture with a pure noble metal powder.

The method of applying an electrically conductive paste to a substrate to produce an electrode is generally used, and the same applies when an electrically conductive paste using the noble metal-coated piezoelectric or electrostrictive ceramic particles of the present invention is used. Can be processed into an electrode.

[0032]

【Example】

[Example 1] --- Palladium-coated PZT (Pb (Zr,
Manufacture of Ti) O ₃ ) fine powder (1) Manufacture of PZT fine powder coated with primary palladium: 5.0 g of PZT titanate fine powder (Pb (Zr, Ti))
O ₃ , an average particle size of 0.5 μm, a specific surface area of 2.1 m ² / g) and 4 ml of an aqueous solution of ammonium tetrachloropalladate (concentration of 1 g / 100 ml in terms of metallic palladium) were added to 200 ml of pure water. Then, a primary dispersion liquid in which barium titanate fine powder was dispersed in an aqueous solution of ammonium tetrachloropalladate was prepared. While stirring this primary dispersion at room temperature, 3 ml of an aqueous solution of hydrazine hydrate (1 ml of 100% hydrazine hydrate was added to 10 ml of this).
(Diluted with 0 ml of pure water) was added. By the addition of this aqueous hydrazine hydrate solution, a trace amount of metallic palladium was uniformly deposited on the surface of the PZT fine powder, and palladium primary-coated PZT fine powder was produced.

(2) Production of PZT fine powder of secondary coating of palladium PZT fine powder of primary coating of palladium was taken out and dried, and then uniformly dispersed in an aqueous solution of hydroxyethyl cellulose (0.2 g / 500 ml). ,
Suspended. This dispersion was then mixed with an aqueous solution of tetraamminepalladium chloride (metal palladium (Pd)
(15 g in terms of) was added to prepare a secondary dispersion. Then, while the secondary dispersion was being stirred, an aqueous hydrazine hydrate solution (containing 4.5 ml of 100% hydrazine hydrate) was slowly added thereto at room temperature. By adding this hydrazine hydrate aqueous solution, PZT fine powder having a black-grey coating layer was obtained. This was separated by filtration, washed with water, and then dried to obtain a dry fine powder. When the dried fine powder (secondarily coated particles) was observed with a scanning electron microscope, it was confirmed that the powder was a homogeneous powder with almost no aggregation. The secondary coated particles consisted of 75 wt% metallic palladium and 25 wt% PZT.

Palladium-coated PZT fine powder 12.5 parts by weight, palladium metal powder 32.5 parts by weight, ethyl cellulose 3.8 parts by weight, dibutyl phthalate 3.8 parts by weight,
Then, 42.5 parts by weight of butyl carbitol was kneaded using a three-roll mill to obtain a conductive paste. Further, a conductive paste was obtained in the same manner by using 50 parts by weight of palladium metal powder without using the palladium-coated PZT fine powder. The obtained conductive paste is printed on the PZT green sheet (unbaked substrate) by screen printing, dried at 100 ° C. for 30 minutes, and then dried over 5 hours to 105.
Heated to 0 ° C. Then, after heating and firing at this temperature for 1 hour, it was cooled. Table 1 shows the appearance and electrical characteristics (resistance value) of the surface of the obtained electrode. Further, a laminated piezoelectric actuator [50 layers, electrode spacing 200 μm (after firing)] was manufactured by the simultaneous firing method using the above conductive paste. A three-point bending test (Sample 1) at a breaking stress of 10 MN / m ² of this laminated piezoelectric actuator was performed.
The destruction probability at 0) was investigated. The results are also shown in Table 1.

Table 1 ──────────────────────────────────── Conductive powder Resistance value (mΩ / sq.) Outside probability of destruction ──────────────────────────────────── Palladium-coated PZT fine powder + Pd metal Powder 80 Good 0% ──────────────────────────────────── Pd Metal powder only 75 Electrode peripheral part Peeling 50% ────────────────────────────────────

[Example 2] -Production of palladium-coated PZT fine powder (1) Production of palladium primary-coated PZT fine powder Example 1 was changed except that the amounts of the respective materials used were changed as follows.
PdT-coated PZT fine powder was prepared in the same manner as in (1). PZT fine powder (same as Example 1): 4.0 g Ammonium tetrachloropalladate aqueous solution (same as above): 3.2 ml Pure water: 200 ml (same as above) Hydrazine hydrate aqueous solution (same as above): 1.5 ml (2) Palladium di Production of Next Coated PZT Fine Powder Example 1 except that the amount of each material used was changed as follows:
PdT secondary-coated PZT fine powder was produced in the same manner as in (2). Hydroxyethyl cellulose: 0.2 g / 500 ml
(Same as Example 1) Tetraamminepalladium chloride aqueous solution: 16 g
(Metal Pd equivalent) Aqueous hydrazine hydrate solution: 4.8 ml (100% hydrazine hydrate equivalent) The obtained PZT fine powder having a black gray coating layer was filtered off, washed with water, and then dried to obtain a dry fine powder. Got When the dried fine powder (secondary coated particles) was observed with a scanning electron microscope, it was confirmed that the powder was a homogeneous powder with almost no aggregation. The secondary coated particles consisted of 80% by weight metallic palladium and 20% by weight PZT.

A conductive paste was prepared in the same manner as in Example 1 using the above-mentioned palladium secondary-coated PZT fine powder, and then this conductive paste was used as an electrode and a laminated piezoelectric actuator by the simultaneous firing method. As a result of evaluation as a conductive powder, almost the same results as those in Example 1 were obtained.

[Example 3] -Production of platinum-coated PZT fine powder (1) Production of platinum primary-coated PZT fine powder (1) of Example 1 except that the materials and the amounts used were changed as follows. Platinum primary-coated PZT fine powder was produced in the same manner as in. PZT fine powder (the same as in Example 1): 3.0 g Ammonium tetrachloroplatinate aqueous solution (aqueous solution having a concentration of 1 g / 100 ml in terms of metal Pt): 1.5 ml Pure water: 200 ml (same as above) Hydrazine hydrate aqueous solution (Same as above): 1.0 ml (2) Production of platinum secondary coated PZT fine powder Example 1 except that the amount of each material used was changed as follows:
A platinum secondary coated PZT fine powder was produced in the same manner as in (2). Hydroxyethyl cellulose: 0.2 g / 500 ml
(Same as Example 1) Tetraammineplatinum chloride aqueous dispersion: 17 g (metal Pt conversion value) Hydrazine hydrate aqueous solution: 4.5 ml (100% hydrazine hydration conversion) PZT fine powder having the obtained black gray coating layer The powder was filtered off, washed with water and then dried to obtain a dry fine powder. When the dried fine powder (secondary coated particles) was observed with a scanning electron microscope, it was confirmed that the powder was a homogeneous powder with almost no aggregation. The secondary coated particles consisted of 85% by weight platinum and 15% by weight PZT. A conductive paste was prepared from the above-mentioned platinum secondary-coated PZT fine powder in the same manner as in Example 1, and then the conductive paste was used to form an electrode by the simultaneous firing method and a laminated piezoelectric actuator. As a result,
Good results have been obtained.

[0039]

EFFECT OF THE INVENTION By using a conductive powder in which a conductive metal material coating layer is formed around the piezoelectric or electrostrictive ceramic particles of the present invention, an electrode and a piezoelectric or electrostrictive actuator (particularly a laminated type) are used. Can be manufactured while reducing the amount of precious metal used and suppressing peeling of the electrode layer.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of the configuration of a typical laminated piezoelectric or electrostrictive actuator.

FIG. 2 is a schematic view showing an example of the configuration of another typical laminated piezoelectric or electrostrictive actuator.

[Explanation of symbols]

 11 Electrode Layer (Internal Electrode Layer) 12 Piezoelectric or Electrostrictive Ceramic Layer 13 External Electrode 21 Electrode Layer (Internal Electrode Layer) 22 Piezoelectric or Electrostrictive Ceramic Layer 23 External Electrode 24 Insulator

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical indication location H01L 41/09 (72) Inventor Yoshihiro Kobayashi 1-1, Suzuki-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Ajinomoto Central Research Institute Co., Ltd. (72) Inventor Nori Nakanishi 1-1, Suzuki-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Ajinomoto Co., Ltd. Central Research Institute

Claims (6)

[Claims] 1. A conductive powder comprising a piezoelectric or electrostrictive ceramic particle and a conductive metal material coating layer formed around the particle. Wherein said piezoelectric or electrostrictive ceramic particles _{are, PbTi0 3, Pb (Zr,} Ti) O 3, (Pb,
La) (Zr, Ti) O ₃ or Pb (Mg _1/3 N
The conductive powder according to claim 1, which is a particle of a metal oxide represented by b _2/3 ) O ₃ or a metal oxide containing these metal oxides as a main component. 3. The conductive powder according to claim 1, wherein the ceramic particle component phase is substantially absent on the outer surface of the conductive metal material coating layer. 4. A conductive paste containing the conductive powder according to claim 1, 2, or 3. 5. A piezoelectric or electrostrictive actuator having an electrode layer formed from the conductive powder according to claim 1. 6. The laminated piezoelectric or electrostrictive actuator according to claim 5, wherein the electrode layers and layers made of piezoelectric or electrostrictive ceramic are alternately laminated.