Moniliform silica sol, process for producing the same, and ink-jet recording medium

A stable silica sol having an SiO2 concentration of 5 to 40% by weight, and containing liquid-medium dispersed moniliform colloidal silica particles having a ratio (D1/D2) of a particle diameter D1 (as measured moniliform colloidal silica particles by a dynamic light scattering method) to a mean particle diameter D2 (as measured spherical colloidal silica particles by a nitrogen absorption method) in a range of 3-50, wherein D1 is 50 to 500 nm, and D2 is 10 to 80 nm, and metal oxide-containing silica bonding these spherical colloidal silica particles, and wherein the spherical colloidal silica particles link in rows in only one plane, obtained by a process comprising the steps (a), (b), (c), and (d) below:

• (a) adding an aqueous solution containing one or more compounds selected from the group consisting of water-soluble II valent metal salts and water-soluble III valent metal salts to an active silicic acid having an SiO2 concentration of 0.5 to 10% by weight and a pH of 2 to 6 or an acidic silica sol having a mean particle diameter of 3 to 8 nm, an SiO2 concentration of 0.5 to 10% by weight and a pH of 2 to 6, in an amount of 1 to 10% by weight as a metal oxide (MO in the case of the II valent metal salt and M2O3 in the case of the III valent metal salt, wherein M represents a II valent or III valent metal atom and O represents an oxygen atom) based on SiO2 in said active silicic acid-containing aqueous colloid liquid or said acidic silica sol, and mixing them;
• (b) adding an acidic spherical silica sol having a mean particle diameter of 10 to 80 nm and a pH 2 to 6 to the mixed liquid (a) obtained in the step (a), a weight ratio (A/B) of a silica content (A) (as derived from said acidic spherical silica sol) to a silica content (B) (as derived from the mixed liquid (a)) of 5 to 100, to an SiO2 concentration of 5 to 40% by weight as a total silica content (A+B), and mixing them;
• (c) adding one compound selected from the groups consisting of alkali metal hydroxides, water-soluble organic bases and water-soluble silicates to the mixed liquid (b) obtained in the step (b) to a pH of 7 to 11, and mixing them;
• and
• (d) heating the mixed liquid (c) obtained in the step (c) at 100 to 200° C. for 0.5 to 50 hours.