Process for producing fine silver particle colloidal dispersion, fine silver particle colloidal dispersion, and conductive silver film

A fine silver particle colloidal dispersion of a water-organic solvent system, which comprises having water and an organic solvent as solvents, containing fine silver particles dispersed in a concentration of from 10 to 70% by weight, containing no polymeric dispersing agent, and having viscosity having been controlled within the range of from 1 to 1,000,000 mPa·s, said organic solvent comprising dimethyl sulfoxide, which has been produced by a process for producing a fine silver particle colloidal dispersion of a water-organic solvent system which comprises:

• a reaction step of allowing an aqueous silver nitrate solution to react with a mixed solution of an aqueous iron(II) sulfate solution and an aqueous sodium citrate solution to form an agglomerate of fine silver particles;
• a filtration step of filtering the resultant agglomerate of fine silver particles to obtain a cake of the agglomerate of fine silver particles;
• a dispersion step of adding pure water to the cake to obtain a first fine silver particle colloidal dispersion of a water system in which dispersion the fine silver particles have been dispersed in the pure water;
• a concentration and washing step of concentrating and washing the first fine silver particle colloidal dispersion of a water system to obtain a second fine silver particle colloidal dispersion of a water system;
• and
• a dilution and viscosity modifying step of adding an organic solvent to the second fine silver particle colloidal dispersion of a water system, wherein
• after the concentration and washing step, the second fine silver particle colloidal dispersion of a water system, when subjected to ultrafiltration, has an ultrafiltrate that has an electric conductivity of 200 μS/cm or less, and
• in the dilution and viscosity modifying step, said organic solvent comprises dimethyl sulfoxide.