JPS639646B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for preventing gelling of a conductive paint useful for forming internal electrodes of ceramic multilayer capacitors. In general, the manufacturing method of multilayer capacitors is such that a conductive material made of conductive metal powder and an organic vehicle is placed on an unfired dielectric sheet formed using a dielectric composition in which ceramic dielectric powder is uniformly dispersed in an organic vehicle. An electrode layer is formed by screen printing a color paint, then a desired number of unfired dielectric sheets with electrode layers made in the same manner are stacked, and finally a dielectric sheet with no electrodes printed is stacked. Either the dielectric composition and the conductive paint are alternately screen printed and dried to form a multilayer structure having alternating dielectric layers and electrode layers. The unfired laminate thus obtained is cut into a predetermined size and then fired at a sufficient temperature,
External electrodes are formed on the sides of the integrated laminate to complete the multilayer capacitor. Alkaline earth metal titanates, lead zirconate, etc. are commonly used as dielectrics, but in order to obtain a dielectric with a high dielectric constant, it is necessary to heat these dielectrics to a temperature that sufficiently sinters them. It is usually fired at a high temperature of over 1000℃. Therefore, the metal component of the internal electrode must be able to withstand this temperature, and high melting point metals such as platinum and palladium are mainly used. However, although platinum is used as a metal component and has excellent electrical properties, it has a high melting point and must be heated to around 1500°C to form internal electrodes. The disadvantage is that the degree of freedom of choice is significantly lost. Particularly in recent years, there has been a trend to use ceramic dielectrics that are generally sintered at low temperatures, but in this case platinum paint cannot be used. On the other hand, when a conductive paint containing palladium powder dispersed in a vehicle is used, the palladium undergoes rapid grain growth during firing, resulting in large sintered grains, a rough and uneven fired surface, and electrode shrinkage. It is extremely difficult to form a good electrode. Moreover, recently, dielectrics to which a small amount of bismuth is added are often used in order to lower the firing temperature and improve the electrical properties of capacitors, but if this is combined with a palladium electrode and co-fired, the bismuth-palladium bond will be better. No reaction occurs. Therefore, palladium electrodes cannot be used at all with bismuth-containing dielectrics. Further, palladium electrodes are not particularly used for high frequencies because, after firing, a portion of the palladium on the surface layer of the electrode remains oxidized at the contact portion with the dielectric layer, and the resistance value of this portion increases. For this reason, conductive paints have been proposed that use a mixture of platinum powder and palladium powder as the metal component. This platinum-palladium paint solves all of the problems mentioned above and is extremely superior to conductive paints that use platinum or palladium alone, but it lacks storage stability as a paint. ,
It has the disadvantage that it cannot be stored for a long period of time. That is, during storage, the paint loses its fluidity and becomes jelly-like, making printing impossible. In order to solve this problem, the present inventors investigated the resin-solvent system used as a vehicle, and found that this gelation phenomenon occurs even with ethyl cellulose, which is generally considered to be the most stable vehicle. Paints containing only platinum powder or palladium powder dispersed in a vehicle hardly cause gelation. However, gelation occurs very quickly due to the coexistence of fine platinum powder and palladium powder in the paint.
The present inventors thought that the reason why such a phenomenon occurs is that the coexistence of platinum and palladium produces a kind of synergistic effect similar to a polymerization catalyst, and polymerizes resins, solvents, etc. Furthermore, attempts were made to change the particle size of the metal powder and to coat the powder with a resin in advance, but none of these methods could improve the storage stability. The object of the present invention is to obtain a conductive paint for internal electrodes of multilayer capacitors that takes advantage of the advantages of platinum-palladium paints and also solves the problem of gelation. That is, the present invention relates to a conductive paint for multilayer capacitor internal electrodes consisting of platinum powder, palladium powder, and an organic vehicle, which is characterized in that the palladium powder is oxidized in advance. This is a prevention method. By pre-oxidizing the palladium powder blended with the platinum powder, the stability of the paint is significantly improved, and there is almost no increase in viscosity even after long-term storage, making it possible to store the paint for a long time. The reason for this is, according to the inventors' clarification, that when palladium powder is oxidized, unlike when platinum powder and palladium powder coexist, no polymerization catalytic action occurs on resins, solvents, etc. This is thought to be due to the The palladium oxide used in the present invention may be produced by any method, but for example, palladium powder can be annealed and oxidized at about 600°C. Particles having a particle size of 0.1 to 10 μm are used, and a particle size in the range of 0.3 to 1 μm is particularly suitable. The platinum powder and organic vehicle may be those commonly used in the art and are not particularly limited. Platinum powder with a particle size of 0.1 to 10 μm, particularly 1 to 5 μm gives good results. Example 1 Platinum powder (average particle size 3 μm) 10 parts by weight Palladium oxide powder (average particle size 0.5 μm)
90 parts by weight Ethyl cellulose 6 parts by weight Terpineol 34 parts by weight Mineral spirits 20 parts by weight The above composition was mixed in a roll mill to obtain a paste-like conductive paint. The initial viscosity of this paint at 25°C was 290 poise. When a gelation acceleration test was conducted at 35°C, the viscosity was 300 poise even after 30 days, showing almost no change in viscosity and being extremely stable. Example 2 A conductive paint was obtained in the same manner as in Example 1, except that 30 parts by weight of platinum powder and 70 parts by weight of palladium oxide powder were used. As shown in Table 1, the storage stability was very good. Example 3 A conductive paint was obtained in the same manner as in Example 1, except that 50 parts by weight of platinum powder and 50 parts by weight of palladium oxide powder were used. As shown in Table 1, the storage stability was very good. Example 4 A conductive paint was produced in the same manner as in Example 1, except that 70 parts by weight of platinum powder and 30 parts by weight of palladium oxide powder were used. The test results are shown in Table 1. Example 5 A conductive paint was produced in the same manner as in Example 1 except that 90 parts by weight of platinum powder and 10 parts by weight of palladium oxide powder were used. The test results are shown in Table 1. Comparative Example 1 Platinum powder (average particle size: 3 μm) 10 parts by weight Palladium powder (average particle size: 0.5 μm) 90 parts by weight Ethyl cellulose 6 parts by weight Terpineol 34 parts by weight Mineral spirits 20 parts by weight The above composition was mixed in a roll mill to make a paste. A conductive paint of the shape was obtained. The initial viscosity was 300 poise. When a gelation acceleration test was carried out at 35°C in the same manner as in Example 1, it exceeded 1000 poise after 7 days.
It became unsuitable for screen printing. Comparative Example 2 A conductive paint was obtained in the same manner as in Comparative Example 1, except that 50 parts by weight of platinum powder and 50 parts by weight of palladium powder were used. The results of the initial viscosity and gelation acceleration tests are shown in Table 1. Comparative Example 3 A conductive paint was obtained in the same manner as in Comparative Example 1, except that 90 parts by weight of platinum powder and 10 parts by weight of palladium powder were used. The results of the initial viscosity and gelation acceleration tests are shown in Table 1.

[Table] As is clear from Table 1, gelation of the conductive paint for internal electrodes of platinum-palladium multilayer capacitors is effectively prevented by the method of the present invention.

Claims (1)

[Claims] 1. A method for preventing gelation of a conductive paint for internal electrodes of a multilayer capacitor comprising platinum powder, palladium powder, and an organic vehicle, which comprises oxidizing the palladium powder in advance.