JP3339225B2 - Method for producing palladium powder for paste - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a conductive paste using palladium (Pd) powder, in particular, a Pd powder for a Pd paste used for forming internal electrodes of a multilayer ceramic capacitor (hereinafter referred to as MLCC).

[0002]

2. Description of the Related Art As electronic components become lighter and thinner, MLCCs, which are chip components, are increasingly required to be reduced in size and increased in capacity. The most effective means for reducing the size and increasing the capacity of the MLCC is to reduce the thickness of the internal electrodes and the dielectric layers to achieve a multilayer structure.

[0003] An MLCC is usually created as follows.

First, barium titanate (BaTiO ₃ )
A dielectric green sheet made of a dielectric powder typified by the above and an organic binder such as polyvinyl butyral is prepared. Next, Pd paste is printed on the surface of the green sheet using a screen printing method or the like to form internal electrodes.
After drying, the internal electrode and the green sheet are laminated so that they alternately overlap with each other, thermocompression-bonded, cut into a desired size, and fired at about 1300 ° C. to remove the binder.
Sintering of the internal electrode and the dielectric is performed. And silver (Ag)
Etc. are formed.

[0005] The Pd paste used here is composed of Pd powder as an electrode forming component, a cellulose resin or an acrylic resin, and an organic binder component such as trimethylbenzene or terpineol as a solvent. Manufactured.

Various production methods are known for this Pd powder. Above all, a wet reduction method in which a reducing agent such as hydrazine is allowed to act on an aqueous Pd solution to precipitate Pd powder is widely used because of its cost and simple reactor. For example, JP-A-3-277706 discloses a combination of an aqueous solution of a tetraammine palladium salt and a hydrazine compound aqueous solution, and JP-A-1-270808 discloses a combination of an aqueous solution of palladium nitrate and an aqueous solution of L-ascorbate.

When Pd powder produced by these methods is subjected to thermogravimetric measurement (TG-DTA) from room temperature to 1000 ° C. at a constant rate, PdO is formed at about 300 ° C. or more in the firing process. Almost 100% P at about 700 ℃
It can be confirmed that the phase changes to dO and returns to the Pd phase again at about 820 ° C. or higher. According to the result of TG measurement of the change in the oxidation rate per hour at a constant temperature of 500 ° C. in air, it was confirmed that the oxidation of the Pd powder progressed rapidly with time. This is said to be a phenomenon which occurs because PdO is a stable phase thermodynamically at about 820 ° C. or lower in the atmosphere, and Pd is a stable phase at about 820 ° C. or higher.

For this reason, Pd using such Pd powder
Since the paste is sensitive to oxidation, it undergoes linear expansion and rapid contraction due to oxidation and reduction of the Pd powder during the MLCC production firing process. And linear expansion is theoretically 820
It approaches 15% near ℃.

The rapid volume change due to the redox of Pd and the rapid heat generation due to the burning of the polymer resin as the binder component of the Pd paste occur at the interface between the internal Pd electrode and the dielectric layer. It is believed that the thermal expansion causes stress due to the difference in thermal expansion, and peeling, swelling and cracks occur at the interface. These defects are called delamination, and are a serious problem particularly in manufacturing a multilayer MLCC.

It is generally known that the larger the crystallite, the higher the oxidation resistance. Therefore, Pd powder is ML
Pd with large crystallite is Pd as material for CC internal electrode
There is a strong demand for pastes.

[0011]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is preferable that Pd suitable as a Pd paste raw material is less oxidized during firing.
It is an object to provide a method for producing d powder.

[0012]

According to the present invention, as a production method for obtaining the above-mentioned Pd powder, a compound which is soluble in an acid even after a heat treatment at 300 ° C. or higher is mixed with a Pd powder. After heat-treating , Pd powder excellent in oxidation resistance is synthesized by dissolving components other than Pd with an acid and separating and recovering only the Pd powder. Specifically, the particle size is 0.1
１1 μm of Pd powder , an acid-soluble compound, and an organic solvent are kneaded, the organic solvent is volatilized and removed, and the obtained mixture of the Pd powder and the acid-soluble compound is heated at 300 ° C. or more, Then, the mixture is allowed to cool, the compound is dissolved with an acid, and the Pd powder is recovered. And preferably, as an easily acid-soluble compound, sodium oxide, sodium hydroxide, calcium oxide, sodium carbonate, barium carbonate, strontium carbonate, calcium acetate, calcium nitrate, sodium chloride, magnesium chloride and other alkali metals or alkaline earth metals. Using oxides, hydroxides, inorganic salts, organic salts, and the like, these are added in equal amounts or more in weight ratio with Pd powder,
As the organic solvent, a lower alcohol such as ethynole alcohol or a solvent for paste, for example, α-terpineol is used.

[0013]

The present invention will be specifically described below.

The Pd powder to be treated in the present invention is not particularly limited. However, considering that the thickness of the internal electrode layer of the multilayer capacitor is about 1 to 3 μm, the particle diameter is 0.1 to 1 μm.
It is desirable to use a Pd powder of μm . In the method of the present invention, the Pd powder is kneaded with an acid-soluble compound and an organic solvent, and then the organic solvent is volatilized and removed.
Heat treatment at a temperature of 00 ° C. or higher, then allow to cool, dissolve the compound with an acid, and recover the Pd powder.By doing so, defects such as lattice irregularity of the Pd powder particles are reduced,
This is because the crystallinity can be improved.

The acid-soluble compound that can be used in the present invention must be soluble in an acid even after being subjected to a heat treatment at 300 ° C. or higher. Compounds that meet this condition include oxides of alkali metals or alkaline earth metals,
Hydroxides, inorganic salts, organic salts and the like. Specific examples include sodium oxide, sodium hydroxide, calcium oxide, sodium carbonate, barium carbonate, strontium carbonate, calcium acetate, calcium nitrate, sodium chloride, magnesium chloride and the like. These compounds and Pd
The mixing ratio with the powder only needs to be such that sintering can be prevented during the heat treatment, and may be an amount that can achieve this purpose. Preferably, the weight ratio is 1: 1 or more.

Examples of usable organic solvents include lower alcohols such as ethyl alcohol and solvents for pastes,
For example, α-terpineol is used. For mixing and kneading of Pd powder and these compounds, use a ball mill,
A letter-shaped blender, a three-roll mill or the like can be used.

In the heat treatment, the organic solvent is removed in advance. This is to prevent bumping or the like due to rapid heating. It is also desirable to lower the oxygen partial pressure so that Pd is not oxidized during the heat treatment. The heat treatment temperature must be at least 300 ° C.
Even if heat treatment is performed at the following temperature, oxidation resistance can hardly be improved. In the method of the present invention, the heat history that the temperature has risen to 300 ° C. or more is important, and is not significantly affected by the heating time.

The acid for dissolving the mixture after heat treatment is P
Any compound that does not dissolve d may be used, and hydrochloric acid is preferred.
The dissolution method is not particularly limited, and it is most convenient to put the mixture after the heat treatment into the acid solution. After dissolution, solid-liquid separation and drying are performed to obtain only Pd powder.

[0019]

Next, an embodiment of the present invention will be described.

(Example 1) (Production of Pd powder) 30 g of Pd powder (product name SFP-801P, average particle size 0.8 μm) manufactured by Sumitomo Metal Mining Co., Ltd.
And 30 g of calcium carbonate powder (special grade reagent) manufactured by Kanto Chemical Co., Ltd., and α-terpineol 10 as a solvent.
g and kneaded well in a watch glass to form a paste. Further, this paste-like mixture is kneaded with a three-roll mill,
A Pd paste was obtained. This Pd paste was transferred to a glass beaker and dried in a vacuum drier for about 12 hours to evaporate the solvent to obtain a mixture of Pd powder and calcium carbonate powder.

Next, this mixture was placed in a porcelain crucible and placed in an electric furnace capable of adjusting the atmosphere. After the inside of the electric furnace was evacuated, nitrogen gas was introduced into the electric furnace, and heat treatment was performed under the conditions shown in Table 1. The oxygen partial pressure in the furnace was measured with a zirconia sensor.

After the heat treatment, the mixture was taken out of the furnace, and the mixture was poured into 500 ml of a 10% hydrochloric acid solution to dissolve CaO in the mixture. After the addition, the mixture was stirred for 30 minutes, filtered, and Pd powder was separated and collected. Collect the recovered Pd powder again to 50
Pour into 0 ml of 10% hydrochloric acid solution, filter and 500 ml
Was washed three times with distilled water and then washed three times with pure water, and dried with hot air at 80 ° C. to obtain Pd powder.

(Evaluation of Pd Powder) Fifty particles were randomly selected from the obtained Pd powder, and the particle diameter was measured by a scanning electron microscope. Then, the average is obtained, and this is calculated as P
d The average particle diameter of the powder was used.

Also. Residual calcium was measured by ICP analysis.

The oxidation characteristics of the Pd powder were determined using a thermogravimetric analyzer (T
G-DTA) to evaluate the maximum oxidized weight increase (W (%)). The maximum oxidation weight increase (%) was in accordance with the following equation.

W (%) = (W _oxd −W _int ) × 100 / W _int Here, W is the maximum oxidized weight increase, and W _oxd
Is the maximum weight measured during the measurement, and W _int is the weight before the measurement. The measurement conditions were as follows: a sample amount of 20 mg, a heating rate of 20 ° C./min, and a measuring temperature range of 25 ° C. to 125 ° C.
0 ° C., air flow rate 100 ml / min.

The maximum weight increase of palladium is theoretically 15%.

The crystallite diameter was measured using a powder X-ray diffractometer (RAD-rVD, manufactured by Rigaku Corporation) and a Cu target and 1 deg. DS (divergence slit). , RS (light receiving slit) 0.3 mm, SS (scattering slit) 1 de
g. Using a slit of voltage 40kV, 150mA,
Scan speed 2 deg. / Min. Was measured. The measurement surface measures the Pd (111) peak and uses computer software (RAD-B system application software K
The crystallite diameter was calculated by the Scherrer method using the Kα1 profile separated by the α1, Kα2 peak separation program). The Scherrer equation R =
For B in 0.9 · λ / (B · cos θ), B2 = Bm2-Bs2 is adopted, R is crystallite diameter, λ is X-ray wavelength, θ is diffraction angle,
Bm is the half width of the measured peak, and Bs is the spread by the optical system obtained in advance from the standard sample. As a standard sample, α-quartz having a particle size of about 0.25 μm annealed at about 800 ° C. was used. In this method, the crystallite diameter is 1
If it exceeds 2,000 angstroms, an error is large and an accurate value cannot be obtained.

The obtained results are shown in Table 1. Sumitomo Metal Mining Co., Ltd.'s unprocessed SF for comparison
The values of P-801P and SFP-501P are also described. As can be seen from Table 1, almost no residual calcium was recognized, and the crystallite size was all 900 Å or more, and the maximum oxidation rate was reduced by almost 40% as compared with the untreated product.

[0030] (Example 2) 30 g of Pd powder (SFP-801P), calcium carbonate (Kanto Chemical's special grade reagent), strontium carbonate (Kanto Chemical's special grade reagent), barium carbonate (Kanto Chemical special grade reagent) and 100 g of ethyl alcohol are shown in Table 2. According to the blending, the mixture was charged into a mixer and mixed for 30 minutes to prepare a mixed slurry. This slurry was transferred to a container and dried at 80 ° C. for 1 hour in a vacuum dryer to obtain a mixture of Pd powder and carbonate. This mixture was heat-treated under the temperature conditions shown in Table 2, and washed under the same conditions as in Example 1 to obtain a Pd powder.

The obtained Pd powder was measured for particle diameter, alkaline earth metal content and maximum oxidized weight increase in the same manner as in Example 1. The alkaline earth metal content was <0.0
The particle size of No. 15 was only 1.1 μm, and the other particles were all 0.8 μm. The obtained results are also shown in Table 2.

[0032] From Table 2, it can be seen that the Pd powder of this example also has extremely high crystallinity, a crystallite diameter of 800 Å or more, and a maximum oxidation amount of 9% or less, exhibiting extremely excellent oxidation resistance.

[0033]

From the above results, the Pd powder obtained by the present invention is characterized by having a large crystallite diameter and excellent oxidation resistance. Therefore, when this powder is used as a silver paste for an MLCC internal electrode. In addition, an effect of preventing delamination occurring at the interface between the internal Pd electrode and the dielectric layer, which is the largest defect of the MLCC, can be expected.

Continuation of the front page (56) References JP-A-6-306401 (JP, A) JP-A-6-96995 (JP, A) JP-A-5-98305 (JP, A) JP-A-6-290633 (JP) JP-A-6-168839 (JP, A) JP-A-51-20761 (JP, A) JP-A-56-13401 (JP, A) JP-A-52-81005 (JP, A) 55-152101 (JP, A) JP-A-62-107001 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22F 1/00-1/02 H01B 13/00 H01G 4 / 12

Claims (3)

(57) [Claims] A kneaded mixture of a Pd powder having a particle size of 0.1 to 1 μm, an acid-soluble compound and an organic solvent, and then the organic solvent is volatilized and removed. A method for producing a palladium powder for a paste, comprising heating a mixture at a temperature of 300 ° C. or higher, then allowing it to cool, dissolving the compound with an acid, and collecting a Pd powder. 2. Use is made of at least one of oxides, hydroxides, inorganic salts and organic salts of alkali metals or alkaline earth metals as readily acid-soluble compounds, and at least one of lower alcohols and terpineols as organic solvents. The method according to claim 1, wherein: 3. The acid-soluble compound is at least one of sodium oxide, sodium hydroxide, calcium oxide, sodium carbonate, barium carbonate, strontium carbonate, calcium acetate, calcium nitrate, sodium chloride, and magnesium chloride. Is added to the Pd powder in an amount equal to or greater than the weight of the Pd powder.
Or the production method according to 2.