Highly crystalline silver powder and production method of highly crystalline silver powder

Abstract

Object of the present invention is to provide a production method of a highly crystalline silver powder containing powder particles in fine particle region and having a good particle size distribution as well as the highly crystalline silver powder obtained by the production method. In order to achieve the object, the present invention adopts a production method characterized in that the method comprises preparation of a first aqueous solution in which gelatin, silver nitrate and nitric acid are dissolved in water, preparation of a second aqueous solution in which L-sorbic acid and / or ascorbic acid and a water-soluble organic acid are dissolved, adding of the second aqueous solution slowly to mix with the first aqueous solution, stirring of the mixture to grow the silver particles after finishing the mixing, keeping of the mixture still to settle the silver particles, discarding of the supernatant, filtration and rinsing to obtain the highly crystalline silver powder.

Description

TECHNICAL FIELD[0001]The present invention relates to highly crystalline silver powder among the silver powders and production method of the highly crystalline silver powder.BACKGROUND ART[0002]Conventionally, highly crystalline silver powder (which has a large crystal diameter) has been widely used for processing into silver ink and silver paste for the reason that it is excellent in thermal shrinkage resistance at the time of sintering. For example, it has been used in wiring circuit of printed wiring board, via hole filling, adhesive for mounting devices and the similar applications in which a silver powder is mixed and cured with various kinds of resin components as well as applications in which a silver powder is sintered at relatively high temperatures such as circuit formation by co-sintering with a ceramic substrate. Silver powder excellent in thermal shrinkage resistance at the time of sintering has been demanded from the point of view for improving accuracy of shape as a c...

AI Technical Summary

Benefits of technology

[0029]The production method of the highly crystalline silver powder of the present invention is suitable for the production of the highly crystalline silver powder whose particles have fine diameter to large diameter by using a water-soluble organic acid together with a reducing agent. In particular, the process is hard to be affected by process changes such as temperature variation, concentration variation at the time of the reductive reaction and the process enables production of the highly crystalline silver powder at a high yield.

Problems solved by technology

L ascorbic acid, which is used as a reducing agent in the production method disclosed in above Patent Document 4 relating to high crystalline silver powder, is expensive and may result increasing of the product price.

However, when fine silver powder particles having a particle diameter less than 2 μm with a crystal diameter of more than 400 Å are aimed, lack of process stability of the production method may result wide variation in the crystal diameter.

Further, it has been confirmed in many case that the fine particles cannot satisfy thermal shrinkage resistance because shrinkage factor after sintering of the fine silver powder particles less than 2 μm is too large.

They are strongly odorous substances, and therefore, it may pollute the working atmosphere as well as causing a problem of accelerated damage on the apparatuses made of copper applied in the facilities.

Besides, the method uses a hydrogen peroxide aqueous solution whose ability tends to change largely and lacks in stability of the quality of the solution.

Therefore, the average particle diameter of the obtained silver powder deviates significantly and controlling of the particle size and particle size distribution is difficult.

As described above, the highly crystalline silver powder consisting of fine particles has been demanded but there has not been the highly crystalline silver powder which sufficiently satisfies market needs.