JPS5919961B2 - Method for producing organic solvent coated palladium powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a conductive composition used in the field of thick film circuit technology,
In particular, the present invention relates to a method for producing organic solvent-coated palladium powder useful as a conductive composition for internal electrodes of multilayer capacitors.

Generally, the manufacture of multilayer capacitors involves forming a dielectric layer, such as a green dielectric sheet, which is formed using a dielectric composition in which alkaline earth metal titanate or lead zirconate is uniformly dispersed in an organic vehicle. An electrode layer is formed by a stencil screen method, and then a desired number of unfired dielectric sheets having electrode layers made by a similar method are stacked and pressurized, or the dielectric composition and the conductive composition are combined. are alternately printed and laminated using a stencil screen method to create a multilayer structure with alternating dielectric layers and electrode layers.

Then, the multilayer capacitor is completed by firing at a sufficient firing temperature and finally forming external electrodes. The firing temperature at this time mainly depends on the dielectric composition used, but
Generally, in order to obtain a multilayer capacitor with a high dielectric constant, 1
The temperature is 200° C. or higher, and for this reason, the conductive metal itself in the conductive composition for electrodes used must be able to sufficiently withstand this firing temperature. That is, in the multilayer capacitor obtained as a result of firing at 1200°C or higher, layer separation (delamin
ation), cracks, and coalescence due to melting of conductive metals. For this reason, various conductive compositions for internal electrodes of multilayer capacitors have been researched in order to meet the above requirements, but none of them have been satisfactory.

For example, conductive compositions using palladium or platinum as the conductive metal are used to withstand temperatures of 1200°C or higher, but although these compositions prevent coalescence due to melting, they cannot eliminate layer separation and cracks. Therefore, it cannot be said that it can withstand the above firing temperature.

As is well known, palladium and platinum have extremely high catalytic activity and store and adsorb large amounts of gas, particularly hydrogen, nitrogen and oxygen. For this reason, when the organic vehicle decomposes in the electrode layer and dielectric layer during firing, it exhibits a local catalytic action and causes a violent decomposition reaction, which causes blistering and shrinkage due to foaming, resulting in a defective finished product. It causes layer separation and cracks in some multilayer capacitors.
In particular, this becomes a big problem when an organic vehicle is decomposed and volatilized from a multilayered structure such as a multilayer capacitor. In addition, blistering and shrinkage due to rapid desorption of occluded and adsorbed gases during firing also cause layer separation and cracks.

Furthermore, in the case of conductive compositions using palladium, palladium is oxidized at around 300 to 800° C. during firing to become palladium oxide and undergoes volumetric expansion.

Then, as the firing temperature increases, it is reduced to palladium again and shrinks. Volume changes such as expansion and contraction also cause cracks and layer separation. Patent Application Publication No. 100566 of 1975 discloses a conductive composition using pre-oxidized palladium oxide in order to eliminate the cracks and layer separation caused by the above-mentioned volume change of palladium. Although some improvements were made, satisfactory results were still not obtained due to the inability to eliminate volumetric contraction due to the reduction of palladium oxide to palladium at temperatures above 800° C. and the presence of occluded and adsorbed gases.

In recent years, there has been a trend towards miniaturization, and the same is true for multilayer capacitors, which consist of a thinner dielectric layer using finer dielectric powder and a thinner electrode layer using finer conductive metal powder. Multilayer capacitors have been attempted, but palladium oxide generally has a large powder size and is difficult to form into a thin film.

The present invention relates to a method for producing palladium powder that eliminates the above-mentioned conventional drawbacks.

More specifically, the present invention relates to a method for producing palladium powder that does not cause foaming, volumetric expansion, or contraction during firing that causes cracks and layer separation.

That is, the method for producing organic solvent-coated palladium powder of the present invention is characterized in that crystallized palladium that has been degassed under vacuum at 350° C. or lower is further coated with an organic solvent. .

Since the palladium powder produced by the present invention is degassed, it does not foam during firing, shrink or bulge due to gas desorption, and as a result provides an excellent multilayer capacitor without cracks or layer separation. . Furthermore, the powder after degassing has weaker agglomeration than that before degassing and can be easily made into fine particles, making it easier to form a thin film. Furthermore, since palladium is coated with an organic solvent, dispersion into an organic vehicle when preparing a conductive composition can be carried out extremely well. In addition, since long-term layer separation could be prevented, the volumetric expansion and contraction of palladium itself in the present invention is thought to be extremely small. The palladium powder used in the present invention before degassing is one that passes through a 325-mesh sieve, preferably one having a particle size of 10 μm or less.

The degassing treatment is first performed at room temperature under vacuum, and then gradually heated to 350° C. or lower, for example, 300° C.

It should be noted that degassing treatment at 350° C. or higher is accompanied by particle growth.

The degassed palladium is further coated with an organic solvent to improve dispersion in an organic vehicle and to prevent gas re-occlusion and re-adsorption.

The organic solvent is selected to be compatible with the organic vehicle component in which the palladium powder is to be dispersed, and is particularly suitable if it is a solvent in the organic vehicle component. Preferably, uniform coating is achieved by first coating with a low boiling point solvent that is easy to coat, then coating with a high boiling point solvent, and then removing the low boiling point solvent by evaporation. In this case, there are no particular restrictions on the type of low boiling point solvent. When using the palladium powder produced in the present invention in a conductive composition, there are no particular restrictions on the organic vehicle, and any commonly used organic vehicle may be used. Metals such as silver and further inorganic binders may be added as appropriate depending on the firing temperature and purpose.

Example 80% hydrazine hydrate solution 330 in palladium chloride solution 21 (containing 1009 as palladium metal) at room temperature
d was added to produce palladium powder.

When the obtained palladium powder was dried, thoroughly pulverized, and observed under an electron microscope, what appeared to be primary particles of about 0.3 to 0.8 μm were found here and there, but most of the particles were 1.1 μm. It was a cloud-like aggregate of ~6.6μ with extremely poor dispersibility.

Further, the results of X-ray analysis did not show a clear diffraction pattern of palladium. This palladium powder is placed under vacuum, first degassed at room temperature, and when the degree of vacuum reaches 10-3 m H9 or less, the temperature is gradually raised, and further degassing treatment is performed at 300 ° C until the degree of vacuum reaches 10-311 H9, The temperature was lowered to room temperature and then brought to liquid nitrogen temperature, and the following organic solvent coating treatment was performed.

Chloroform, which had been previously degassed and kept at room temperature, was introduced in an amount sufficient to coat the palladium surface, and then warmed to room temperature to obtain palladium powder wetted with chloroform.

Next, while keeping the temperature at room temperature, butyl carbitol which had been degassed in advance was poured in, and only chloroform was evaporated under vacuum at room temperature to obtain butyl carbitol-coated palladium powder. Example of use The following conductive composition was manufactured using the organic solvent coated palladium powder obtained in the example.

A barium titanate dielectric composition was printed on an alumina substrate by a stencil screen method and dried, and then the above conductive composition was printed and dried by the same method.

These operations were repeated alternately to form 30 dielectric layers and 30 electrode layers.Finally, a dielectric layer was formed by the same method and was peeled off from the substrate and divided into individual blocks. Firing was performed at a temperature increase rate of 200°C/hour to 800°C, and held at 800°C for 3 hours. The temperature was further raised to 1400° C. in the same manner, held at 1400° C. for 4 hours, and then gradually cooled to room temperature to obtain a multilayer capacitor. As a result, no cracks or layer separation were observed in the 50 multilayer capacitors obtained by the same method, and there were no practical problems in all of them.

Furthermore, it was confirmed by X-ray analysis that the palladium powder obtained in the present invention was completely crystallized, and the ease with which aggregates were loosened was compared to that of palladium before degassing in the example. The particles were dispersed into particles of 0.2 to 0.7 μm (possibly primary particles) by pulverization in a mortar for about 1 minute.

Furthermore, the palladium of the example had a volume reduction of 20% due to the degassing treatment.

This seems to be due to the desorption of occluded and adsorbed gas. Comparative Example 1 The palladium powder used in Example 1 was exposed to air for 7 hours without degassing or coating with an organic solvent.
When 50 multilayer capacitors were manufactured in the same manner except that palladium oxide was obtained by oxidation at 00°C for 1 hour and this was replaced with the palladium powder used in the usage example, 40 had cracks and layer separation that made them unusable. .

This was due to contraction of the electrode layer at 800-900°C. Comparative Example 2 Fifty multilayer capacitors were manufactured in the same manner as in the usage example except that the palladium powder used in the example was used without degassing and without being coated with an organic solvent. Layer separation occurred.

As is clear from the above results, by using the organic solvent-coated palladium powder produced by the method of the present invention, it was possible to produce an excellent multilayer capacitor free from cracks and layer separation.

Claims (1)

[Claims] 1. A method for producing organic solvent-coated palladium powder, which comprises further coating crystallized palladium powder that has been degassed at 350° C. or lower under vacuum with an organic solvent.