| 摘要 |
It is an object of the present invention to obtain a composite sol capable of forming an ink-receiving layer having a high transparency and a high property for fixing dyes. The present invention provides a sol which is a colloidal solution having aggregate particles containing silica and alumina dispersed in an aqueous medium, wherein the silica is such that the primary particles are spherical and the average particle size of the primary particles is from 2 to 200 nm, the average particle size of the aggregate particles is at least twice the average particle size of the silica primary particles and at most 1,000 nm, the zeta-potential of the aggregate particles is at least +10 mV, and the pH of the solution is from 3 to 9. The present invention provides a method for producing a silica-alumina composite sol, which comprises gradually adding an aluminum salt of which the liquid exhibits acidity when dissolved in water, to a silica sol, and a method for producing a silica-alumina composite sol, which comprises mixing a silica sol with an alumina sol having a specific surface area of a xerogel obtainable by drying of at least 150 m<2>/g, to form aggregate particles containing silica and alumina, followed by peptization treatment.
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