JPH02243769A - Method for manufacturing conductive particles - 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 Field of Industrial Application The present invention relates to a method for producing conductive particles used as electrode materials.

Conventional technology Conventionally, conductive paints consisting of conductive particles, resins, and solvents (including trace amounts of frit, metal oxides, and organometallic oxides in some cases) have been widely used as electrode materials for various parts. ing. Here, as the conductive particles,
Expensive precious metals such as gold, silver, platinum, and palladium are used, and in order to reduce the cost of electrode materials, efforts are being made to reduce the amount of precious metals used or replace them with base metal materials.

Copper and nickel have been used for full replacement with base metal materials, and silver-copper alloys have been used for partial replacement, but in both cases, oxides are formed when baked in air or left unattended, making them conductive. To prevent burning, the atmosphere must be controlled and the electrode surface must be coated.
There is a problem that the manufacturing process becomes complicated. On the other hand, in order to reduce the amount of precious metals used, attempts have been made to coat base metal particles with noble metals as a base material (for example, Japanese Patent Publication No. 46-40593, Japanese Patent Application Laid-open No. 6O-10O).
Publication No. 679).

When a conductive paint using such noble metal coated particles is applied to a ceramic material and baked in air to form an electrode, the coated noble metal is not sintered in a continuous state and the base material is exposed. However, due to the generation of oxides, the conductivity decreases. In order to prevent this, the coating thickness of the noble metal must be increased, and the cost reduction effect is suppressed. In fact, in order to suppress the exposure of the base material, improvements have been made to the plating method when coating precious metals (for example, Japanese Patent Publication No. 61-22O5.28).
.

However, when baking at high temperatures, when base metal particles are coated with noble metals as a base material,
Basically, it is impossible to completely suppress heat diffusion from the base material to the coated metal, so in order to suppress the exposure of the base material, the thickness of the coated noble metal must be increased.
or Fib. Significant cost reductions cannot be expected.

Further, the use of oxides such as silicon oxide, aluminum oxide, vanadium oxide, zirconium oxide, or barium titanate as the base material has also been considered (for example, Japanese Patent Publications No. 61-22O5.29 and No. 48586).

However, when such oxides are used, thermal diffusion to the noble metal layer is suppressed compared to base metals, but since all of the above oxides are insulators, it is difficult to maintain conductivity as an electrode material. However, the coating thickness must be increased by 62 mm, making it difficult to significantly reduce material costs. Furthermore, the specific resistance of the obtained electrode is high because the base is an insulator, and it cannot be used as an electrode material for electronic components that require high frequency characteristics.

Problems to be Solved by the Invention Regarding the conductive particles having the above-mentioned structure, in which the base material is a base metal or an oxide and is coated with a noble metal, baking at high temperatures prevents the base material from being exposed or the conductivity from decreasing due to processing. In order to achieve this, the thickness of the coating must be increased, which increases the amount of precious metal used, and there is a problem that the cost of the conductive particles cannot be significantly reduced.

The present invention has been made in view of this point, and an object of the present invention is to provide conductive particles having excellent conductivity and thermal stability at a low cost.

Means for Solving the Problems In order to solve the above problems, the method for producing conductive particles of the present invention includes a structure in which the surfaces of conductive composite oxide particles are coated with a noble metal colloid.

Here, as the conductive composite oxide, especially Ll-1sr
xCo03 (o1≦X≦O,a).

Pr1-xSrXCoo5 (0.2≦X≦0.8).

Nd 1-2 Sr x Go O3 (0.3≦X≦0
．． 7).

La1-xBaxCoo3 (0.1≦x≦0.6).

Pr1 zBaxCo03 (0.2≦X≦0.5), having one or more of the following compositions, or La2-xSrxCu04 (01≦X≦O, S
).

La2 zBaxCu04 (001 ≦
Those having a u2O5.5,5 composition are preferred.

Effect: Due to the above-described structure of the present invention, since the base material is a conductive oxide, diffusion into the coating precious metal layer is suppressed, and the coating thickness can be made very thin, resulting in a significant cost reduction. . In addition, the characteristics resulting from the chemical stability of the coated noble metal layer include dielectric materials and magnetic materials. It is possible to suppress the deterioration of the dielectric properties or magnetic properties of the ceramic material and the deterioration of its conductivity as an electrode.

Further, in the present invention, a composite oxide is used as the base material because the composite oxide is superior in terms of conductivity and cost compared to an oxide containing a single metal element.

In particular, La1-1srxCoo3(0.1≦x≦0.s
).

Pr1.5rxCoo3 (0.2≦x≦0.s).

Nd1-1srxCoo5 (03≦X≦07).

La1-xBaxC003 (0.1≦x≦0.is)
.

Pr1. One having a composition of one or more of BaxCoo3 (0.2≦X≦0.5), or La2-xSrXCu04 (01≦X≦o5).

Those having a solid solution composition of one or more of La2-xBaxCub4 (0.01≦x≦0.5), as well as YBa2Cu3O7 system, BiCaS
r Cu 2 O 5.5,5 system compositions all have excellent conductivity, and high conductivity can be obtained even if the thickness of the noble metal coating is thin, making it possible to significantly reduce the cost of conductive particles. It is possible.

Furthermore, as a method for coating a base material with a noble metal, a noble metal colloid is attached to the surface of particles of a conductive oxide. This method allows the thinnest and most uniform noble metal layer to be applied, has strong adhesion, and does not cause detachment of the noble metal colloid from the surface of the particles even when dried.
It is also excellent in mass production.

Examples of noble metals that can be coated include gold, silver, palladium, platinum, rhodium, ruthenium, and alloys thereof. In addition, when coating with noble metals, it is also possible to coat with two or more of the above noble metals in multiple layers.

Example Hereinafter, the present invention will be explained in detail with reference to Examples.

(Example 1) Using La2O5.3, SrCO3, and Co3O4 as starting materials, the required amounts of each were weighed, mixed in ethanol for 12 hours, dried, and then calcined at 900°C. Next, after pulverizing the calcined powder, it was fired at 1000°C for 2 hours to obtain La (1,5S
Conductive particles having a composition of r(1,5CoO3) were obtained.

On the other hand, palladium chloride as a palladium colloid is dissolved in water together with 5 moles of sodium chloride.

Next, a surfactant is added to the mixture while stirring, and then an aqueous solution of sodium borohydride is added dropwise to the mixture. Palladium colloid is instantaneously produced, giving it a black color. Here, as the surfactant, any type of cationic, anionic, or nonionic surfactant may be used. In this example, the nonionic surfactant used was a nonionic surfactant (trade name: LD-11 manufactured by Lion Yushi Co., Ltd.).
0) was added. In this colloid solution, the above L
Conductive particles having a composition of IL0.5SrO, 5COO3 are introduced while being dispersed in a magnetic cooler. After stirring and mixing for about 1 hour, the solution became transparent and contained palladium colloid 10, - in the conductive particles.

is absorbed. After the palladium colloid was adsorbed, the particles were washed with water by decantation and dried to obtain palladium-coated conductive particles. The weight ratio of the conductive particles thus obtained to the palladium colloid coating film was as shown in Table 1 below. Next, the palladium-coated conductive particles 1
A mixture consisting of 00 parts by weight of glass frit, 5 parts by weight of glass frit, 2 parts by weight of ethyl cellulose, and 10 parts by weight of α-terepinol was kneaded using three rolls to obtain an electrode paste. After screen printing this electrode paste on an alumina substrate, 1
The baking process was carried out at 00°C for 10 minutes. The electrical resistance of the thick film baked in this way was as shown in Table 1, indicating excellent electrical conductivity.

(Table 1 below) On the other hand, La(15SrO.5GoO3 was evaluated as an electrode paste under the above conditions using conductive particles not coated with palladium.The measurement results are shown in Table 1 above. 1>.

These results show that when using Lao5Sro5C003 alone as an electrode, it does not have sufficient stability during sintering in terms of reaction stability. Therefore, the palladium colloid coating increases the conductivity of the particles and suppresses the reaction between the base material and the alumina substrate, which is the substrate material.The two effects combine to create conductivity on the alumina substrate. It can be seen that an excellent thick film is formed.

(Example 2) La2O5.3, Pr6041, Nd2O5.3
, BaCO3, SrCO3, Go,04 as starting materials, La1-z
srxCOO5, Pr1, SrxCoo3, Nd
1-zsrxCoo, , La1 zBaxCo05
, Pr1-xBa4co03, powders with different X of each composition system were prepared. Using these conductive particles as a base material, noble metal colloid treatment was performed in the same manner as in Example 1, and the weight ratio of the base material and palladium colloid was 2O5.
/1 palladium-coated particles were obtained. Using these conductive particles, a conductive paste was prepared in the same manner as in Example 1, and the paste was baked onto an Albana substrate and the electrical resistance value was measured. The results of converting this measured value into Ωcm are shown in Table 2 below.

(Margin below) T ■. 11111 × × × × × ■ 〒〒の. 111 × × × × × ト■ ト■ ト〒 〒 〒 〒 〒 ト． 11111 × × × × × ■ Tori■ 〒 〒 〒 〒 10. 11111× × × × × pust size ■ ■ 〒 〒 〒 〒 〒の． 1111× × × × × ■ ■ ■ ■ 〒 〒 〒 〒 〒 〒 〒 〒 〒 〒 . 11111O × × × × × ■ to ■ 〒 〒 ○ ``. １１１１× × × × × １■ ■ へ〒〒 T １○ ○ ○ ０． 11111 × × × × × O Toto, / Q 13/, -ノ14. From the results in Table 2 above, it can be seen that the electrical resistance value of the baked thick film is determined not only by the coated palladium but also by the composition of the base material. Palladium also plays a role in preventing reactions with ceramic materials.

However, in order to obtain excellent conductivity, the composition of the base material must be La1-xSrxCoo3 (0.1≦X≦os
) , pr1zsrxCoo3( 0 2≦x≦os)
,Nd1 zsrxCoo3(0 3≦X≦07),L
a1-zBaxCo03 (0 1≦X≦06), Pr
l zBaxCoo3 (0.2≦X≦o.ts).

Next, using an oxide composite of the above materials as a base material, the palladium colloid was coated in the same manner as above, and the electrical resistance of the resulting thick film was measured. As shown in Table 3, excellent conductivity was confirmed.

(Left below in white) <table 3〉 15A-.

The weight ratio is 2O5. /1. Next, a conductive paste was prepared using the platinum colloid-coated particles in the same manner as in Example 1, baked on an alumina substrate at a temperature of 900° C., and the electrical resistance was measured. The results of converting this measured value into units of 9 cm are shown in Table 4 below.

(Left below) (Example 3) Using La2O5.3, SrCO3, BaCO3, and CuO as starting materials, the required amounts of each were weighed, mixed in ethanol for 12 hours, dried, and fired at 900'C for 2 hours. ,
Heat treated in oxygen at 600°C to form La2-xSrxCu0
Conductive particles having compositions in which X of 4°La2 zBaxCu04 was variously changed were obtained. This powder is immersed in a platinum colloid liquid to adhere the platinum colloid to the surface of the conductive particles. The base material of the obtained particles and platinum 17.

18/, 7 From the results in Table 4, in order to obtain excellent conductivity, the composition of the base material should be La2-xSrxCub4 (0.1≦x≦0.s)
.

LIL2-xB&xcu04 (001≦X≦0.6)
is found to be suitable. Next, a platinum colloid was attached using an oxide composite of the above materials as a base material in the same manner as above, and then paste-forming and baking were performed, and the electrical resistance value of the obtained thick film was measured. As a result, excellent conductivity was confirmed as shown in Table 5 below.

<Table 5> (Example 4) Y2O2, BaCO3, CuO, Bi2O5, CaCO
Using 3゜SrCO3 as a starting material, weigh the required amount of each, mix in ethanol for 12 hours, and after drying 197, -
7 After firing at 850°C for 2 hours, heat treatment was performed in oxygen at 600°C to obtain YBa2Cu30. Bi Ca Sr C
u2O5. Conductive particles having a composition of s and s were obtained. The particles are immersed in a gold colloid liquid to adhere the gold colloid to the surface of the conductive particles. The weight ratio of the base substance and gold of the particles thus obtained is 2O5. /1. A conductive paste was prepared using the gold colloid-coated particles in the same manner as in Example 1, and was placed on an alumina substrate with 850%
It was baked at a temperature of °C and its electrical resistance was measured. As a result, the electrical resistance value when the base material is YBa2Cu3O7 is 5 to 6 × 10 Ωcm, and BiCaSrCu2O
5.5. In the case of s, it was 7 to 8×10 Ωcm, and excellent conductivity was confirmed.

(Example 5) Magnesium lead niobate [Pb (Mg1/3Nb2/
3) o3] to 100 parts by weight of dielectric powder containing as the main component,
8 parts by weight of polyvinyl butyral resin, Schiftylf pv-
4 parts by weight of trichloroethane, 40 parts by weight of trichloroethane, and 25 parts by weight of butyl acetate were added and mixed for 2Q hours in a ball barrel.

The dielectric slurry thus obtained was formed into a sheet with a thickness of 4 0 μm using a reverse roll method. Next, by the same method as in Example 1, I, a a, s Sr O, 5Go
Conductive particles whose surfaces are coated with palladium colloid (weight ratio of Lao5Sro5C003 and palladium: 2O5./1) are prepared, ethyl cellulose and α-televinol are added thereto, and the mixture is kneaded with a triple roll to form an electrode paste. It was created.

This electrode paste was printed on the dielectric sheet, cut into desired dimensions, and baked at 1000° C. for 2 hours. The side surface of the thus obtained sintered body where the electrode is exposed is coated with a palladium colloid prepared in the same manner as in Example 1.Lao,5SrO,sCoO.

(Weight ratio of La 11.5 Sr 11.5 Go O3 and palladium: 2O5./1) An electrode paste consisting of Tokarasufurisoto, ethyl cellulose, and α-terevisionol was applied and baked at 80°C.

The capacitance value of the multilayer chip capacitor obtained in this way agrees well with the design value calculated from the dielectric constant (ε=12O5.00), and the capacitance value of the multilayer chip capacitor obtained in this way agrees well with the design value calculated from the dielectric constant (ε=12O5.00). -2 The practicality of the electrode was confirmed. In addition to this example, it goes without saying that conductive composite oxide particles coated with noble metal colloids have practical applications as electrodes for chip resistors, chip inductors, varistors, piezoelectric elements, and even ceramic multilayer wiring boards. stomach.

Since all of the composite oxides targeted by the present invention usually have oxygen vacancies, the composition of oxygen is not particularly defined. Furthermore, in order to control the chemical stability or electrical properties of the base material, metal elements or anionic elements other than the main component elements may be added to the base material. Furthermore, the composite oxide particles used in the above examples were o
Although the particle size was in the range of 1 to 5.0 μm, the particle size and shape are not particularly defined.

On the other hand, it goes without saying that silver, rhodium, iridium, ruthenium, and alloys thereof, which can be coated with a colloid, may be used in addition to the above embodiments as the noble metal colloid.

Effects of the Invention As described above, the present invention provides conductive particles having a structure in which particles 227 of a conductive composite oxide are coated with noble metal colloid, and have excellent conductivity and thermal and chemical stability. Excellent conductive particles can be produced at low cost, and are of great practical value.

Claims (1)

[Scope of Claims] (1) A method for producing conductive particles, characterized in that the particle surface of a conductive composite oxide is coated with a noble metal colloid. (2) The conductive composite oxide is La_1_-_xSr_xC
oO_3 (0.1≦x≦0.8), Pr_1_−_xS
r_xCoO_3(0.2≦x≦0.8)Nd_1_-
_xSr_xCoO_3 (0.3≦x≦0.7), La
_1_-_xBa_xCoO_3(0.1≦x≦0.5
), Pr_1_−_xBa_xCoO_3(0.2≦x
The method for producing conductive particles according to claim 1, characterized in that the conductive particles have a solid solution composition of one or more of the following: ≦0.5). (3) The conductive composite oxide is La_2_-_xSr_xC
uO_4(0.1≦x≦0.5)La_2_−_xBa
2. The method for producing conductive particles according to claim 1, wherein the conductive particles have a solid solution composition of one or more of _xCuO_4 (0.01≦x≦0.5). (4) The method for producing conductive particles according to claim 1, wherein the conductive composite oxide has a YBa_2Cu_3O_7 composition. (5) The conductive composite oxide is BiCaSrCu_2O_5
＿． The method for producing conductive particles according to claim 1, characterized in that the conductive particles have a composition of _5 series. (6) An electrode for electronic components, characterized in that the conductive particles according to claim 1 are used.